Abstract:
Excess oxygen in the combustion process of a facility that bums carbon-based fuels may cause a visible plume in the atmosphere at the stack of the facility. Traditional optical based opacity monitors may be unable to detect this plume or the plume may form at a location downstream from the opacity monitor toward the stack. The present invention discloses methods to utilize common combustion control variables to detect and signal the presence of a visible plume of exhaust gasses. Also disclosed are systems that detect the visible plume and provide a signal so that the combustion process may be manually or automatically adjusted to reduce or eliminate the visible plume.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention generally relates to the detection of a visible plume emitted from smokestacks or chimneys of power generating facilities.  
         BACKGROUND OF THE INVENTION  
         [0002]    Opacity monitors are used in facilities wherein exhaust gasses from the combustion of carbon-based fuels can release pollutants into the atmosphere through the facility&#39;s chimney. Generally, such opacity monitors utilize an optical detection system that measures opaqueness in the stream of exhaust gasses across the chimney or across an exhaust duct leading to the chimney. The opacity monitor creates an electronic signal that is proportionate, either directly or inversely, to the opaqueness detected in the exhaust stream. This electronic signal is used for automatic or manual control of the facility and the combustion process and for other facility operations or reporting purposes.  
           [0003]    Opacity monitors do not have the ability to measure or indicate the appearance of the emission of exhaust gasses from a facility burning carbon-based fuels once such gasses have left the facility&#39;s chimney. Opacity, as measured by an opacity monitor, and the curbside appearance of the visual emissions from the chimney can diverge greatly. Combustion quality is one of the largest contributors to the appearance of chimney emissions. When carbon-based fuels are not completely burned because of a lack of the presence of sufficient oxygen during the combustion process, carbon is exported in the exhaust stream out of the chimney. This condition causes high opaqueness of the exhaust stream whereby it is very visible with a black to dark brown color resulting in a high opacity reading from the opacity monitor. This incomplete burning creates a situation where the correlation between the curbside appearance of exhaust gasses and the measured opacity is accurate.  
           [0004]    Excess oxygen also affects the combustion process. The presence of excess oxygen beyond what is necessary for complete combustion of the fuel results in a plume being emitted from the facility&#39;s chimney. A plume is a visible emission from a facility&#39;s chimney that is light gray to white in color that can be very dense or highly opaque under certain conditions. When this heavy plume is present the correlation between the curbside appearance and the measured opacity is poor. The opacity monitor is unable to detect the plume because its formation occurs further down the exhaust stream than where the opacity monitoring device is located. In fact, the plume is generally formed in the atmosphere after the exhaust gasses leave the chimney.  
           [0005]    Previous attempts to detect the presence of a visible plume have involved the use of optical detection devices to signal the presence of a smoke plume. U.S. Pat. No. 4,320,975 (Lilienfield), for example, involves a device that operates by measuring the proportion of polarized blue light from the background sky which passes through the plume. Unlike the present invention; however, Lilienfield requires the mounting of a device to “look” through the plume, which may be affected by environmental conditions as well as creating maintenance problems. Moreover, Lilienfield fails to address accuracy issues that may be caused by ambient conditions such as nighttime, cloudy days, etc.  
           [0006]    An unsatisfied need therefore exists for systems and methods to determine the presence of an exhaust plume so that such detection can create an electronic signal for the automatic or manual control of the combustion process and to better comply with the United States Environmental Protection Agency&#39;s (“EPA&#39;s”) regulations and guidelines and with other clean-air laws. The opacity monitor is used for this combustion control process but it is overridden when the presence of an exhaust plume is indicated because the two signals (opacity and plume presence) require opposite control action of the same combustion process control variable, excess air. The plume presence signal is developed using combustion related control variable measurements that may be available to a facility&#39;s distributed control system (“DCS”).  
         SUMMARY OF THE INVENTION  
         [0007]    The invention is based, at least in part, on the discovery that the presence of a visible plume of exhaust gasses at the exhaust stack or chimney of a facility burning carbon-based fuels may be detected using parameters of the combustion process rather than relying upon visible detection of the plume itself. Traditional, optical based opacity monitors may not detect plumes caused by excess oxygen in the combustion process. The present invention detects the conditions that make a plume likely and provides a signal than can be utilized to manually or automatically control the combustion process in order to reduce or eliminate the visible plume.  
           [0008]    One aspect of the present invention relates to a system that receives inputs from the combustion process and makes a determination based upon these inputs whether a visible plume of exhaust gasses exist at the facility&#39;s stack. In one embodiment, the system receives at least total air and total fuel flow into the combustion chamber of the facility as inputs. The system calculates a ratio of total air flow to total fuel flow and compares this ratio to a predetermined value to determine the presence of a visible plume. Other aspects of the system may incorporate additional inputs such as one or more of opacity from an opacity monitor, oxygen content and carbon monoxide content in the exhaust stream to increase the accuracy of the detection of the plume. These systems may be incorporated into the facility&#39;s control system or they may stand alone.  
           [0009]    Another aspect of the invention relates to methods for detecting and signaling the presence of a visible plume at the stack of a facility burning carbon-based fuels. These methods rely upon combustion control parameters that may be pre-existing in many power generation facilities. In one embodiment, a method is disclosed to determine the presence of a visible plume from a ratio of the total air and total fuel flow into the combustion chamber of the facility. Other methods may incorporate with the total air flow to total fuel flow ratio additional combustion control parameters such as one or more of opacity from an opacity monitor, oxygen content and carbon monoxide content in the exhaust stream to increase the accuracy of the detection of the plume.  
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)  
       [0010]    Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:  
         [0011]    [0011]FIG. 1 is an illustrative embodiment of a boiler and combustion control system of a facility utilizing a plume presence monitoring system in accordance with the present invention.  
         [0012]    [0012]FIG. 2 is a plume presence circuit, in accordance with an embodiment of the present invention, for use in a dual-fuel power generation facility burning either No. 6 fuel oil and/or natural gas in its boiler.  
         [0013]    [0013]FIG. 3 is an illustrative graph, in accordance with an embodiment of the present invention, illustrating an exemplary curve for determining a level of O 2  in exhaust gasses from a power generation facility for which there is a likelihood of the presence of a visible plume.  
         [0014]    [0014]FIG. 4 is an illustrative graph, in accordance with an embodiment of the present invention, illustrating an exemplary curve for determining a level of CO in exhaust gasses from a power generation facility for which there is a likelihood of the presence of a visible plume.  
         [0015]    [0015]FIG. 5 is a flow chart illustrating an exemplary method to determine the presence of a visible plume at the chimney or stack of a facility burning carbon-based fuels in accordance with the present invention.  
         [0016]    [0016]FIG. 6 is a flow chart illustrating a second exemplary method to determine the presence of a visible plume at the stack of a facility burning carbon-based fuels in accordance with the present invention.  
         [0017]    [0017]FIG. 7 is a flow chart illustrating the second exemplary method to determine the presence of a visible plume at the stack of a power generation facility burning carbon-based fuels in accordance with the present invention at a power generating facility that combusts No. 6 fuel oil as its primary fuel in its boiler.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]    The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout.  
         [0019]    The present invention relates to systems and methods to detect a visible plume of exhaust gasses at the stack of a facility burning carbon-based fuels. Unlike previous systems and methods, the present invention does not attempt to directly detect the plume through only optical means but utilizes combustion control parameters that are generally pre-existing in power generation facilities. Furthermore, the system may readily be incorporated into a facility&#39;s existing control system or it may stand alone as a separate module.  
         [0020]    [0020]FIG. 1 is a simplified schematic of a power generation facility utilizing an embodiment of a plume presence monitoring system in accordance with the present invention. Referring to FIG. 1, a burner  102  provides fuel and air to a boiler  104  for combustion. The boiler  104  provides steam to a steam turbine which is drivingly connected to an electrical generator which produces electrical power. Exhaust gasses from the combustion are routed from the boiler  104  to the stack  106  where they are emitted to the atmosphere. The exhaust gasses may pass through many devices while being routed from the boiler  104  to the stack  106 , including, for example, exhaust ducting  108 , an air heater  110 , an induced draft fan  112 , and an electrostatic precipitator  114 , as each of these are well known in the art. The opacity of exhaust gasses in the stack  106  is monitored by an opacity monitor  116 , which, generally, measure the opaqueness of the exhaust gasses as they pass by an optical detection device and as such opacity monitors are well known in the art. A signal correlated to the measured opacity (“Instantaneous Opacity”) is provided to the facility&#39;s Distributed Control System (“DCS”)  118 . Likewise, carbon monoxide (“CO”) monitors  120  and oxygen (“O 2 ”) monitors  122 , as each are well known in the art, measure the CO and O 2 , respectively, found in the exhaust gasses as they travel toward the stack  106 . These measured CO and O 2  quantities are converted into electrical signals by the monitors  120 ,  122  and the CO signal and O 2  signal are received as inputs into the facility&#39;s DCS  118 .  
         [0021]    Devices as are well known in the art monitor the facility&#39;s total air  124  and total fuel  126  as is provided to the combustion chamber of the boiler  104 . These devices  124 ,  126  convert the measured quantities of air and fuel, respectively, into electrical signals of total air flow and total fuel flow that are input into the facility&#39;s DCS  118 . Alternatively, one or both of the values for total air flow and total fuel flow may be calculated by the DCS  118  from other measured parameters such as, for example, the speed of the induced draft fan  112  and/or the speed of a forced draft fan  128 , and the weight of the fuel being combusted, respectively.  
         [0022]    While FIG. 1 illustrates an embodiment of the invention in a power generation facility with both, induced draft fans  112  and forced draft fans  128 , other embodiments of the invention may be employed in power generation facilities having only one or more induced draft fans  112 , or in power generation facilities having only one or more forced draft fans  128 .  
         [0023]    A ratio of the total air flow to total fuel flow is determined. In one embodiment, if the total air flow sufficiently exceeds the total fuel flow, then there is a high likelihood of a visible plume at the stack  106  of the facility and a plume presence signal will be activated. For example, a 300 megawatt (“MW”) power generation facility burning No. 6 fuel oil in its boiler may have a minimum threshold value for the total air flow to total fuel flow ratio of preferably 1.02. In other words, in this example, if the total air flow to total fuel flow ratio equals or exceeds approximately 1.02, this embodiment of the invention will signal the presence of a visible plume at the stack  106  of the facility. To reduce the likelihood of this embodiment of the system providing a false plume presence signal, other combustion related control variables may be introduced in the system. For example, in an embodiment of the present invention, the likelihood of a false plume presence signal is greatly reduced in a 300 MW power generation facility burning No. 6 fuel oil in its boiler, for example, if, in addition to the total air flow to total fuel flow ratio being greater than or equal to preferably 1.02, the O 2  in its exhaust gasses, as measured by the O 2  monitor  122 , exceeds a threshold limit that is a function of the current MW demand of the generator (i.e., the amount of electrical power currently being produced by the electrical generator); if the CO measured in the exhaust gasses as measured by the CO monitor  120  is less than preferably 100 parts per million (“ppm”); and if the instantaneous opacity as measured by the opacity monitor  116  is, for example, less than or equal to preferably 20 percent. These additional O 2  and CO signals are provided as inputs to the DCS  118  in an embodiment of the present invention and, if the conditions indicated above are present, the system will provide a plume presence signal that has a much greater likelihood of correctly signaling the presence of a plume than if the system relied only upon the total air flow to total fuel flow ratio.  
         [0024]    The embodiment of the system illustrated in FIG. 1 can be used to manually or automatically adjust the combustion process in the event the presence of a plume at the stack  106  of the power generation facility is indicated by the a plume presence signal from the system. The signal can be used to alert an operator to adjust any one or any combination of fuel flow, induced draft fans  112 , or forced draft fans  128  to reduce or eliminate the visible plume. Likewise, the plume presence signal can be utilized by the DCS  118  to automatically adjust any one of or any combination of fuel flow, induced draft fans  112 , or forced draft fans  128  to reduce or eliminate the visible plume.  
         [0025]    [0025]FIG. 2 illustrates an embodiment of a logic circuit for detecting and signaling the presence of a visible plume at the chimney or stack of a dual-fuel power generation facility that is capable of combusting No. 6 fuel oil and/or natural gas in its boiler. This circuit provides a logical Boolean output of “TRUE” or a “1” if a visible plume is present at the stack of the facility. This output can be used to automatically or manually adjust the combustion process in order to eliminate or reduce the visible plume.  
         [0026]    Generally, and as explained in detail below, this circuit operates by determining if a moving average  202  of the instantaneous opacity  204  of the exhaust gasses is less than or equal to a predetermined value, such as approximately 20 percent in the present embodiment; if a moving average  206  of the total air flow  208  into the boiler divided by the total fuel flow  210  into the boiler is greater than or equal to a predetermined value, such as approximately 1.02 in the present embodiment; if a moving average  212  of the lowest O 2  percentage reading  214 ,  216 , as determined by comparing  218  one or more O 2  inputs  214 ,  216 , as such inputs are obtained from the exhaust gas stream of the facility, is greater than a maximum normal O 2  percentage, as such maximum normal O 2  percentage is determined as a function  220  of the current MW demand  222  of the facility; and, if the moving average  224  of the greatest CO percentage reading  226 ,  228 , as determined by comparing  230  one or more CO inputs  226 ,  228 , as such inputs are obtained from the exhaust gas stream of the facility, is less than a minimum normal CO percentage, as such minimum normal CO is determined as a function  232  of the current MW demand  222  of the facility. If all of the above-recited elements are present, if the circuit is “ON”  234  and if the facility is not burning more than a set percentage of natural gas  236 , the circuit will signal the presence of a visible plume  238  at the stack of the facility.  
         [0027]    The power generating facility employing the exemplary circuit in FIG. 2 is capable of concurrently burning natural gas and fuel oil, or burning each fuel exclusively. Natural gas is a “clean burning” fuel in that it is highly unlikely to produce a visible plume during combustion. In the circuit illustrated in FIG. 2, if the ratio of natural gas to total fuel (natural gas and fuel oil) exceeds a predetermined limit, then the circuit will not signal the presence of a visible plume because the likelihood of a visible plume decreases as the ratio of natural gas to total fuel increases. This natural gas cutoff is controlled by the input “Nat. Gas % Too High”  236  as indicated on FIG. 2. In this illustrative circuit of FIG. 2, if a predetermined value, such as approximately 20 percent or more of the total fuel being combusted in the present embodiment is natural gas, the circuit will not signal the presence of a visible plume  238  because it is highly unlikely that a visible plume will be present when burning natural gas at concentrations equal to or greater than this predetermined value. This “Nat. Gas % Too High”  236  input is illustrative of the flexibility and adaptability of this circuit, is not a required input for the circuit, and is obviously not necessary in facilities that burn only one fuel. Furthermore, the circuit can be activated or deactivated either automatically or manually as indicated by the “ON/OFF” input  234  of FIG. 2.  
         [0028]    The exemplary circuit illustrated in FIG. 2, as well as other embodiments of the invention, may be incorporated into a mechanism consisting of a control system of a facility utilizing the invention. Such a mechanism may consist of one, or a combination of, software, hardware, firmware, DCS, stand-alone devices and components, manual calculations and/or data entry, etc. For example, the logic of this embodiment of the circuit may be programmed into a facility&#39;s DCS and utilize pre-existing DCS inputs such as instantaneous opacity  204 , total air flow  208 , total fuel flow  210 , O 2  inputs  214 ,  216 , current MW demand  222 , CO inputs  226 ,  228 , etc., perform logic operations upon the inputs, and produce or not produce a plume presence signal  238 , depending upon the outcome of the logic operations. Other embodiments of the invention may utilize mechanisms that exist independently of a facility&#39;s control system or are only partially integrated into the facility&#39;s control system. Such a mechanism may consist of one, or a combination of, software, hardware, firmware, a facility&#39;s DCS, a separate DCS, standalone components and devices, manual calculations and/or data entry, etc. For example, the logic of the exemplary circuit in FIG. 2 or in other embodiments of the invention may be incorporated into a separate control module wherein the control module receives inputs such as instantaneous opacity  204 , total air flow  208 , total fuel flow  210 , O 2  inputs  214 ,  216 , current MW demand  222 , CO inputs  226 ,  228 , etc., performs logic operations upon the inputs, and does or not produce a plume presence signal  238 , depending upon the outcome of the logic operations.  
         [0029]    Referring now to the exemplary embodiments of the invention in FIGS. 1 and 2, an opacity monitor  116 , preferably an optical-based opacity monitor as is well-known in the art, detects the opacity of the exhaust gasses at a point upstream from the outlet of the stack  106 . The opacity monitor  116  sends an instantaneous opacity signal  204  to the facility&#39;s DCS  118 , and the instantaneous opacity signal  204  is utilized as an input to the plume presence logic circuit of FIG. 2. In this embodiment, the plume presence logic circuit of FIG. 2 is a part of the DCS  118 , however, the plume presence logic circuit may be a part of any control or processor system or may, as described above, be a separate, stand-alone device. A moving average  202  is taken of the instantaneous opacity  204  input. The average instantaneous opacity  204  must be less than or equal to a predetermined value, such as approximately 20 percent in the present embodiment, before the circuit in FIG. 2 will trigger a Plume Presence Signal  238 .  
         [0030]    A component of the embodiment of the plume presence circuit of FIG. 2 is determining the total air flow  208  to total fuel flow  210  ratio. Total air flow  208  is a measurement of the amount of air flowing into the combustion chamber of the boiler  104  during the power generation process. It is generally a function of the forced draft  128  and/or the induced draft fans  112  of a typical power generation facility. Total fuel flow  210  is a measurement of the fuel flowing into the combustion chamber of the boiler  104  during the power generation process. In the embodiment illustrated in FIG. 2, the fuel is either natural gas, fuel oil, or a combination of the two, but in other power generation facilities the fuel may be coal, coke, heavy oils, petroleum distillates, synthetic fuels, wood, bark, shredded tires, trash, or any other combustible material and any combination of these. Although these fuels may be measured in various units, the DCS  118  generally converts the fuel flow into units compatible with the air flow.  
         [0031]    The moving average  206  of the ratio of the total air flow  208  to total fuel flow  210  must be greater than or equal to a predetermined value, such as approximately 1.02 in the present embodiment, in order to detect the presence of a visible plume with the exemplary circuit illustrated in FIG. 2. A Boolean operator of “TRUE” is sent to an and gate  240  if the ratio of the total air flow  208  to total fuel flow  210  is greater than or equal to the predetermined value. This predetermined value is empirically determined by visually monitoring the stack  106  of the power generation facility at various ratios of total air flow  208  and total fuel flow  210  and recording the values of total air flow  208  and total fuel flow  210  when a visible plume either is, or is not, present. The ratio may vary according to the fuel burned at the power generation facility.  
         [0032]    The power generation facility utilizing the exemplary circuit illustrated in FIG. 2 has two forced draft fans  128  and two induced draft fans  112  that provide air to the combustion chamber in the boiler  104  and create a draft through the boiler  104  and into the stack  106 , respectively, although other power generation facilities may have only one or more forced draft fans  128 , only one or more induced draft fans  112 , or a combination of one or more forced draft fans  128  and one or more induced draft fans  112 . The O 2  content of the exhaust gasses passing through each of the induced draft fans  112  is monitored and provided as inputs to the DCS  118 . O 2  E  214  is the O 2  content in the exhaust gasses passing through the east induced draft fan  112  and O 2  W  216  is the O 2  content of the exhaust gasses passing through the west induced draft fan  112 . The lowest of these two O 2  inputs  214 ,  216  is determined by the O 2  comparison block  218  and the moving average  212  of the lowest O 2  value is determined. This moving average  212  of the lowest O 2  reading must exceed a lower threshold limit as such lower limit is determined as a function of the current MW demand  222  of the facility. Relating the minimum O 2  level where plume presence is likely as a function of the current MW demand  222  of the facility is determined empirically by recording the O 2  level over various ranges of MW demand  222  over time and for numerous combinations of O 2  and MW demand  222 , and visually determining if a plume is present at the stack  106  of the power generation facility at the recorded O 2  level and MW demand  222 . This empirical analysis then allows a curve to be determined whereby if the O 2  level at a certain MW demand exceeds the curve, then there is a likelihood that a plume will be present at the stack  106  of the power generation facility. FIG. 3 is an illustrative example of the appearance of such a curve  300 , as such curve  300  may be determined from empirical analysis. In the illustrative example of FIG. 3, if the O 2  level at a certain MW Demand  222  is on the curve  300 , or in the area above the curve  302 , then there is a greater likelihood of the presence of a visible plume at the stack  106  of the power generation facility than if the O 2  level at the same MW Demand  222  is in the area below the curve  304 . Logically, as illustrated in the exemplary circuit of FIG. 2, the threshold minimum for O 2  is set as a function of current MW demand  222  by the O 2  MW function block  220 .  
         [0033]    Likewise, the CO content of the exhaust gasses passing through each of the induced draft fans  112  is monitored and provided as inputs to the DCS  118 . CO E  226  is the CO content in the exhaust gasses passing through the east induced draft fan  112  and CO W  228  is the CO content of the exhaust gasses passing through the west induced draft fan  112 . The higher of these two CO inputs  226 ,  228  is determined by the CO comparison block  230  and the moving average  224  of this higher CO value is determined. This moving average  224  of the highest CO reading must be less than an upper threshold limit as such upper limit is determined as a function of the current MW demand  222  of the facility. Relating the maximum CO level where plume presence is likely as a function of the current MW demand  222  of the facility is determined empirically by recording the CO level over various ranges of MW demand  222  over time and for numerous combinations of CO and MW demand  222 , and visually determining if a plume is present at the stack  106  of the power generation facility at the numerous recorded CO levels and MW demands  222 . This empirical analysis then allows a curve to be determined whereby if the CO level at a certain MW demand exceeds the curve, then there is a lessened likelihood that a plume will be present at the stack  106  of the power generation facility. FIG. 4 is an illustrative example of the appearance of such a curve  400 , as such curve  400  may be determined from empirical analysis. In the illustrative example of FIG. 4, if the CO level at a certain MW Demand  222  is in the area above the curve  402 , then there is a lesser likelihood of the presence of a visible plume at the stack  106  of the power generation facility than if the CO level at the same MW Demand  222  is on the curve  400 , or in the area below the curve  404 . Logically, as illustrated in the exemplary circuit of FIG. 2., the threshold maximum for CO is set as a function of current MW demand  222  by the CO MW function block  232 . One of ordinary skill in the art will readily recognize that the O 2    122  and CO monitors  120  may be located anywhere in the exhaust gas stream before the gasses exit the stack  106 .  
         [0034]    The moving averages  212 ,  224  of the O 2    214 ,  216  and CO  226 ,  228  inputs are compared to their threshold levels at the process comparison blocks  242  and  244 , respectively. The thresholds for the process comparison blocks  242 ,  244  are set as a function of current MW demand  222 . If the moving average  212  of the lowest O 2  input  214 ,  216  is greater than or equal to its threshold, as compared to such threshold by the O 2  process comparison block  242 , then a Boolean “TRUE” output is provided by the O 2  process comparison block  242 . Likewise, if the moving average  224  of the highest CO input  226 ,  228  is less than or equal to its threshold, as compared to such threshold by the CO process comparison block  244 , then a Boolean “TRUE” output is provided by the CO process comparison block  244 . The outputs of the O 2  process comparison block  242  and the CO process comparison block  244  are each provided as inputs to an and gate  246 . The output of the and gate  246  is provided as an input to the and gate  240 . Though utilizing three logical and gates, one of ordinary skill in the art will readily recognize that the exemplary circuit illustrated in FIG. 2 may be configured with as few as one logical and gate. Furthermore, while FIG. 2 illustrates the use of moving averages  202 ,  206 ,  212 , and  224 , for several inputs, one of ordinary skill in the art will readily recognize that such averages are provided only to increase the stability of the exemplary circuit illustrated in FIG. 2, and that the circuit and its various inputs may be configured with or without such moving averages.  
         [0035]    In an embodiment of the invention as illustrated in the exemplary circuit of FIG. 2, if the logical signals that are input to and gate  240  are “TRUE”, that is if the total air flow  208  to total fuel flow  210  ratio is equal to or greater than a predetermined value such as approximately 1.02; if the lowest O 2  reading  214 ,  216  is greater than or equal to a minimum threshold that is determined as a function of the current MW demand  222  of the facility; if the highest CO reading  226 ,  228  is less than or equal to a maximum threshold that is determined as a function of the current MW demand  222  of the facility; and if the instantaneous opacity  204  of the facility is less than another predetermined value such as approximately 20 percent, and if the circuit “ON” signal  234  is “TRUE,” then the circuit illustrated in FIG. 2 will provide a Boolean “TRUE” output at an and gate  248  which shall constitute a plume presence signal  238  for a power generation facility burning No. 6 fuel oil in its boiler.  
         [0036]    It is to be recognized that although FIGS. 1 and 2 are illustrative of embodiments of the invention applied in a power generation facility that utilizes a boiler to provide steam to a steam turbine that drives an electrical power generator, these embodiments or other embodiments of the invention can be applied in combustion turbine engines, diesel engines, gasoline engines, and other engines or facilities where the combustion of carbonbased fuels may lead to the presence of a visible plume. Embodiments of the invention can also be applied in facilities that are not used for electrical power generation, such as pulp and paper mills, refineries, and other process facilities where carbon-based fuels are burned. The invention would be particularly useful in a combustion turbine power generation facility that utilizes a petroleum product or by-product as a fuel.  
         [0037]    [0037]FIG. 5 is a flow chart illustrating an exemplary method to determine the presence of a visible plume at the chimney or stack of a facility burning carbon-based fuels in accordance with the present invention. In Step  502  of this embodiment, the ratio of the total air flow entering the combustion chamber of a boiler to the total fuel flow that is entering the boiler is compared to a predetermined value. In Step  504 , if the ratio of Step  502  is greater than or equal to the predetermined value, then a plume presence signal is activated in Step  506 . If the ratio of Step  502  is less than the predetermined value, then the process returns to its beginning (Step  500 ) and begins the process anew. For example, in an embodiment of the invention, if the ratio of total air flow to total fuel flow is greater than or equal to approximately 1.02 in a boiler burning No. 6 fuel oil, a plume presence signal  238  will be provided.  
         [0038]    [0038]FIG. 6 is a flow chart illustrating a second exemplary method to determine the presence of a visible plume at the stack of a facility burning carbon-based fuels in accordance with the present invention. In Step  602  of this embodiment, the ratio of the total air flow entering the combustion chamber of a boiler to the total fuel flow that is entering the boiler to a predetermined value. In Step  604 , if the ratio of Step  602  is greater than or equal to the predetermined value, then the process continues on to Step  606 . If the ratio of Step  602  is less than the predetermined value, then the process returns to its beginning (Step  600 ) and begins anew.  
         [0039]    In Step  606 , a measured O 2  value of the exhaust gasses from the combustion is compared to a minimum threshold O 2  value. This minimum threshold O 2  level is established in Block  608  as a function of the rate of combustion which is proportional to the steam being produced by the boiler and the load on the boiler. In Step  610 , if the measured O 2  value is greater than or equal to the minimum threshold O 2  (as established by Block  608 ), then the process continues on to Step  612 , otherwise if the measured O 2  value is less than the minimum threshold O 2  value, then the process returns to its beginning (Step  600 ) and begins anew.  
         [0040]    In Step  612 , a measured CO value of the exhaust gasses from the combustion is compared to a maximum threshold CO value. This maximum threshold CO level is established in Block  614  as a function of the rate of combustion which is proportional to the steam being produced by the boiler and the load on the boiler. In Step  616 , if the measured CO value is less than or equal to the maximum threshold CO (as established by Block  614 ), then the process continues on to Step  618 , otherwise if the measured CO value is greater than the maximum threshold CO value, then the process returns to its beginning (Step  600 ) and begins anew.  
         [0041]    In Step  618 , a measured instantaneous opacity value of the exhaust gasses produced by the combustion is compared to a second predetermined value. In Step  620 , if the measured instantaneous opacity is less than or equal to the second predetermined value, the process moves on to Step  622  and signals the presence of a visible plume. If the measured instantaneous opacity in Step  620  is greater than the second predetermined value, then the process returns to its beginning (Step  600 ) and begins anew.  
         [0042]    [0042]FIG. 7 is a flow chart illustrating the second exemplary method to determine the presence of a visible plume at the stack of a power generation facility burning carbon-based fuels in accordance with the present invention. The exemplary power generation facility illustrated in this embodiment of FIG. 7 has a 300 MW generator driven by a steam turbine and the facility burns No. 6 fuel oil in its boiler. In Step  702  of this embodiment, the ratio of the total air flow entering the combustion chamber of a boiler to the total fuel flow that is entering the boiler to a predetermined value, such as approximately 1.02, in this embodiment. In Step  704 , if the ratio of Step  702  is greater than or equal to the predetermined value of approximately 1.02, then the process continues on to Step  706 . If the ratio of Step  702  is less than the predetermined value of approximately 1.02, then the process returns to its beginning (Step  700 ) and begins anew.  
         [0043]    In Step  706 , a measured O 2  value of the exhaust gasses from the combustion is compared to a minimum threshold O 2  value. This minimum threshold O 2  level is established in Block  708  as a function of the rate of combustion which is proportional to the steam being produced by the boiler and the load on the boiler (and, in this instance, the current MW demand of the electrical generator that is driven by the steam turbine). In Step  710 , if the measured O 2  value is greater than or equal to the minimum threshold O 2  (as established by Block  708 ), then the process continues on to Step  712 , otherwise if the measured O 2  value is less than the minimum threshold O 2  value, then the process returns to its beginning (Step  700 ) and begins anew.  
         [0044]    In Step  712 , a measured CO value of the exhaust gasses from the combustion is compared to a maximum threshold CO value. This maximum threshold CO level is established in Block  714  as a function of the rate of combustion which is proportional to the steam being produced by the boiler and the load on the boiler (and, in this instance, the current MW demand of the electrical generator that is driven by the steam turbine). In this embodiment of the invention utilized on a 300 MW power generation facility that burns No. 6 fuel oil in its boiler, the maximum threshold CO level at 300 MW demand is approximately 100 ppm. In Step  716 , if the measured CO value is less than or equal to the maximum threshold CO (as established by Block  714 ), then the process continues on to Step  718 , otherwise if the measured CO value is greater than the maximum threshold CO value, then the process returns to its beginning (Step  700 ) and begins anew.  
         [0045]    In Step  718 , a measured instantaneous opacity value of the exhaust gasses produced by the combustion is compared to a second predetermined value. In this embodiment of the invention utilized on a 300 MW power generation facility that burns No. 6 fuel oil in its boiler, the second predetermined value is approximately 20 percent. In Step  720 , if the measured instantaneous opacity is less than or equal to the second predetermined value, the process moves on to Step  722  and signals the presence of a visible plume. If the measured instantaneous opacity in Step  720  is greater than the second predetermined value, then the process returns to its beginning (Step  700 ) and begins anew.  
         [0046]    Many modifications and other embodiments of the invention will come to mind to one skilled in the art to which this invention pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.