Abstract:
A signal processing technique that allows the flame signal from a first source of flame and the flame signal from a second source of flame to be discriminated from each other when only both the first and second flame signals are viewed by the same flame scanner. The signal from the flame scanner is processed to enhance one or more of the attributes associated with the first flame and is simultaneously processed to enhance one or more attributes associated with the second flame.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims the priority of U.S. provisional patent application Ser. No. 60/528,736 filed on Dec. 11, 2003, entitled “Signal Processing Technique For Improved Flame Scanner Discrimination” the contents of which are relied upon and incorporated herein by reference in their entirety, and the benefit of 
     
    
     1. FIELD OF THE INVENTION  
       [0002]     This invention relates to industrial flame scanner instrumentation and more particularly to such instrumentation that is required to distinguish, that is, discriminate, flames from different fuels being alternately burned in the same burner or discriminate the flame between burner and adjacent ignitor where the ignitor may be burning the same or different fuel than the main burner.  
       2. DESCRIPTION OF THE PRIOR ART  
       [0003]     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.  
         [0004]     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.  
         [0005]     One requirement in determining if a stable flame exists or if the flame has become unstable or lost is that the flame scanner must be able to discriminate flames between adjacent burners or between burner or ignitor or between different fuels in a burner. One example of a flame scanner that can discriminate flames between adjacent burners is the silicon carbide photodiode based flame scanner described in commonly owner U.S. Pat. No. 6,472,669 (“the &#39;669 patent”) which issued on Oct. 29, 2002. The disclosure of the &#39;669 patent is incorporated herein by reference.  
         [0006]     Common practice in discriminating flames between different burners or between burner and ignitor or between different fuels in a burner, is to design a system that can detect and act upon a flame signal signature that is specific to the fuel type or burner/ignitor mechanical configuration. There are a number of factors that contribute to flame signal signatures. Examples are fuel type, fuel to air ratios, scanner location in relation to flame ignition points, flame profile in relation to the scanner position, flame scanner sighting angle, burner load, and boiler load. All of these factors, and others, combine to create a unique flame signature.  
         [0007]     The art of flame discrimination techniques is in the ability to recognize the differences between the signatures emanating from two flame sources. Most often these differences are minute and lead to marginal discrimination performance. Sometimes the differences between flame sources have overlapping characteristics as the burner or boiler progresses through its operating load range making discrimination impossible during a segment of time.  
         [0008]     Typically, the raw flame scanner signal, as it comes from the scanner head, is conditioned and then processed to detect particular attributes associated with either the fuel or burner for which the scanner is assigned to discriminate. Once an attribute is detected, it is then compared to predetermined trip limits for recognition as flame or no flame. It is desirable to find the associated attributes in a timely and consistent fashion. Examples of typical attributes include intensity, flicker frequency, and AC amplitude.  
         [0009]     In accordance with the present invention the flame signal is conditioned in parallel paths allowing the signal attributes to be enhanced according to the assigned programmed trip settings while at the same time suppressing the attributes of the alternate flame. This conditioning increases the attribute separation, making detection more predictable, timely and consistent.  
       SUMMARY OF THE INVENTION  
       [0010]     A method to discriminate flame between a first flame having a predetermined number of associated flame attributes and a second flame having a predetermined number of associated flame attributes. The first and second flames are viewed by a single flame scanner and the flame scanner produces a signal indicative of the first and second flames. The method: 
        simultaneously processes the flame indicative signal to enhance one or more of the predetermined number of first flame associated flame attributes and to enhance the one or more of the predetermined number of second flame associated flame attributes;     determines when the enhanced one or more of the predetermined number of first flame associated flame attributes exceeds an associated predetermined threshold; and     determines when the enhanced one or more of the predetermined number of second flame associated flame attributes exceeds an associated predetermined threshold.        
 
         [0014]     A fossil fuel fired steam generator that has: 
        a source for producing a first flame, the first flame having a predetermined number of associated flame attributes;     a source for producing a second flame, the second flame having a predetermined number of associated flame attributes;     a flame scanner for viewing both the source of the first flame and the source of the second flame and producing a signal indicative of the first flame and of the second flame;     means for simultaneously processing the flame scanner signal to enhance one or more of the predetermined number of flame attributes associated with the first flame and to enhance the one or more of the predetermined number of flame attributes associated with the second flame; and     means for determining when the enhanced one or more of the predetermined number of flame attributes associated with the first flame exceeds an associated predetermined threshold and when the enhanced one or more of the predetermined number of flame attributes associated with the second flame exceeds an associated predetermined threshold.       
 
     
    
     DESCRIPTION OF THE DRAWING  
       [0020]      FIG. 1  shows a block diagram of a prior art approach to discriminate flames from fuels being alternately burned in the same burner or discriminate the flame between burner and adjacent ignitor where the burner may be burning the same or different fuel than the main burner.  
         [0021]      FIG. 2  shows a block diagram of the approach of the present invention to such flame discrimination. 
     
    
     DETAILED DESCRIPTION  
       [0022]     Referring now to  FIG. 1  there is shown the block diagram of a circuit  10  of the traditional, that is, prior art, approach, when the flame scanner instrumentation is required to distinguish, that is, discriminate, between flames from two sources. The two flame sources may be different fuels being alternately burned in the same burner or the flame between burner and adjacent ignitor where the ignitor may be burning the same or different fuel than the main burner.  
         [0023]     As is shown in  FIG. 1 , in circuit  10  the same conditioned and filtered signal from the flame scanner  12  is passed to circuitry which has the programmable trip points for flame “A”  14  and flame “B”  16 . For example, flame “A” represents a burner flame, and flame “B” represents an adjacent ignitor flame. Flame “A” is known to generate a flame signal with slightly less flicker frequency then flame “B” during some operating conditions but not all operating conditions. This makes discrimination between the two flames impossible over the entire range of operating conditions since the same conditioned and filtered flame signal is used by the trip points for flame “A” and flame “B”.  
         [0024]     In the circuit of  FIG. 1 , the signal from scanner  12  is conditioned at  18  and then filtered by fixed filters  20   a  and  20   b . Fixed filter  20   a  filters the conditioned signal from scanner  12  for intensity using a two pole low pass filter. That intensity filtered and conditioned signal is fed to both trip points for flame A  14  and trip points for flame B  16 . Fixed filter  20   b  filters the conditioned signal from scanner  12  for frequency using a two pole low pass filter. That frequency filtered and conditioned signal is fed through adjustable frequency algorithm  26  to both trip points for flame A  14  and trip points for flame B  16 . Trip points for flame A  14  is connected to trip relay A  22  and trip points for flame B  16  is connected to trip relay B  24 .  
         [0025]     Referring now to  FIG. 2 , there is shown the block diagram for a circuit  30  where the raw flame signal from flame sensor  32  is first conditioned by signal conditioner  34  and then enters a parallel network  36  having branches  38  and  40 . Branch  38  has a programmable filter  42  which processes the conditioned signal in a manner to enhance flame “A” flicker frequencies and branch  40  has a programmable filter  44  which processes the conditioned signal in a manner to enhance flame “B” flicker frequencies. Each parallel programmable filter  42 ,  44  may be programmed to “feature” the raw conditioned flame signal in such a way as to widen the separation between flicker frequency “A” and flicker frequency “B”, thus generating a discrimination signal that is now distinguishable over the entire range of operating conditions.  
         [0026]     Programmable filter  42  comprises digital filters  42   a  which filters the conditioned flame signal for intensity and adjustable frequency algorithm  42   b  connected to the output of: digital filters  42   a . The output of adjustable frequency algorithm  42   b  is connected to trip points A  46  as is one output of digital filters  42   a . Programmable filter  44  also comprises digital filters  44   a  which filters the conditioned flame signal for intensity and adjustable frequency algorithm  44   b  connected to the output of digital filters  44   a . The output of adjustable frequency algorithm  44   b  is connected to trip points B  48  as is one output of digital filters  44   a.    
         [0027]     For a more specific example, consider the case where the scanner must discriminate between an oil flame and a coal flame. The oil flame normally has a characteristically higher flicker frequency then the coal flame. For this example the coal flicker frequency is higher than normal and is approaching the oil flicker frequency making separation of the fuels difficult and only marginally reliable over the entire operation load range using the techniques shown in the conventional circuit  10  of  FIG. 1  as the adjustable frequency algorithm  26  is adjusted to either enhance the high frequency harmonics that are routinely found in the oil flame while suppressing the low frequency harmonics routinely found in the coal flame or enhance the low frequency coal harmonics while suppressing the high frequency oil harmonics.  
         [0028]     However, in the technique shown in the circuit  30  of the present invention, the digitally filtered and conditioned flame signal passes through an adjustable frequency algorithm for example algorithm  42   b , that is adjusted to enhance the high frequencies that are routinely found in the oil flame, while suppressing the low frequency harmonics routinely found in the coal flame.  
         [0029]     In the same fashion, the adjustable frequency algorithm, for example  44   b , on the coal side of the parallel branches  38  and  40 , enhances the low frequency coal harmonics while suppressing the high frequency oil harmonics. Thus the two resulting coal and oil flame signals have the resulting frequencies that are further separated making discrimination between the two more predicable over the entire burner load range.  
         [0030]     In addition to flicker frequency, the present invention can have different trip points for other flame attributes, such as intensity and/or flame signal amplitude. The flame signals may also be conditioned or shaped, that is, pre-processed, using the parallel programmable filters  42  and  44  to enhance individual flame attributes. Examples of such filtering techniques include but are not limited to Fourier analysis, box car averaging, scaling, band pass, low pass or other filter techniques. The conditioning algorithms are configurable such that two separate configurations are executed simultaneously on the same sensor data. Each configuration is used to enhance the differences between the two flames and make it easier to detect the presence of each one.  
         [0031]     In both the traditional approach and the present invention that flame scanner  10  may be embodied for example as described in the &#39;669 patent or may use ionic flame monitoring as is described in commonly owned U.S. Pat. No. 6,356,199 (“the &#39;199 patent”) which issued on Mar. 12, 2002. The disclosure of the &#39;199 patent is incorporated herein by reference.  
         [0032]     It is to be understood that the description of the preferred 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.