Patent Publication Number: US-7581945-B2

Title: System, method, and article of manufacture for adjusting CO emission levels at predetermined locations in a boiler system

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is related to the following United States Patent Applications filed contemporaneously herewith: SYSTEM AND METHOD FOR DECREASING A RATE OF SLAG FORMATION AT PREDETERMINED LOCATIONS IN A BOILER SYSTEM, Ser. No. 11/290,759; and SYSTEM, METHOD, AND ARTICLE OF MANUFACTURE FOR ADJUSTING TEMPERATURE LEVELS AT PREDETERMINED LOCATIONS IN A BOILER SYSTEM, Ser. No. 11/290,244 which are incorporated by reference herein in their entirety. 
   BACKGROUND OF THE INVENTION 
   Fossil-fuel fired boiler systems have been utilized for generating electricity. One type of fossil-fuel fired boiler system combusts an air/coal mixture to generate heat energy that increases a temperature of water to produce steam. The steam is utilized to drive a turbine generator that outputs electrical power. 
   A by-product of combusting an oxygen and a hydrocarbon-based fuel mixture, such an air/coal mixture, is carbon monoxide (CO). One objective of a control system controlling operation of a coal fired boiler system is to maintain total CO levels exiting a boiler system below a threshold level. The inventors herein have recognized that CO levels at particular locations in the boiler system can have CO levels greater than a threshold CO level while other locations have CO levels less than the threshold CO level. Further, the variance of CO levels in the boiler system can result in increased total CO emissions and local CO concentrations above the threshold level. 
   Accordingly, the inventors herein have recognized a need for an improved system and method for controlling a boiler system that can determine locations within the boiler system that have relatively high CO levels and that can adjust an air-fuel (A/F) ratio of burners affecting those locations to decrease CO levels therein. 
   BRIEF DESCRIPTION OF THE INVENTION 
   A method for adjusting CO emission levels within a boiler system in accordance with an exemplary embodiment is provided. The boiler system has a first plurality of burners and a plurality of CO sensors disposed therein. The method includes receiving a plurality of signals from the plurality of CO sensors disposed at a first plurality of locations in the boiler system. The method further includes determining a plurality of CO levels at the first plurality of locations based on the plurality of signals. The method further includes determining a second plurality of locations that have CO levels greater than or equal to a threshold CO level. The second plurality of locations is a subset of the first plurality of locations. The method further includes determining a second plurality of burners in the boiler system that are contributing to the second plurality of locations having CO levels greater than or equal to the threshold CO level. The second plurality of burners is a subset of the first plurality of burners. The method further includes determining an amount of CO being generated by each burner of the first plurality of burners for each location of the second plurality of locations. The method further includes increasing an A/F ratio of at least one burner of the second plurality of burners to increase A/F ratios at the second plurality of locations in order to decrease the CO levels at the second plurality of locations toward the threshold CO level, based on the amount of CO being generated by the at least one burner of the second plurality of burners. 
   A control system for adjusting CO emission levels within a boiler system in accordance with another exemplary embodiment is provided. The boiler system has a first plurality of burners. The control system includes a plurality of CO sensors disposed at a first plurality of locations in the boiler system. The plurality of CO sensors are configured to generate a plurality of signals indicative of CO levels at the first plurality of locations. The control system further includes a controller operably coupled to the plurality of CO sensors. The controller is configured to receive the plurality of signals and to determine a plurality of CO levels at the first plurality of locations based on the plurality of signals. The controller is further configured to determine a second plurality of locations that have CO levels greater than or equal to a threshold CO level. The second plurality of locations are a subset of the first plurality of locations. The controller is further configured to determine a second plurality of burners in the boiler system that are contributing to the second plurality of locations having CO levels greater than or equal to the threshold CO level. The second plurality of burners is a subset of the first plurality of burners. The controller is further configured to determine an amount of CO being generated by each burner of the first plurality of burners for each location of the second plurality of locations. The controller is further configured to increase an A/F ratio of at least one burner of the second plurality of burners to increase A/F ratios at the second plurality of locations in order to decrease the CO levels at the second plurality of locations toward the threshold CO level, based on the amount of CO being generated by the at least one burner of the second plurality of burners. 
   An article of manufacture in accordance with another exemplary embodiment is provided. The article of manufacture includes a computer storage medium having a computer program encoded therein for adjusting CO emission levels within a boiler system. The boiler system has a first plurality of burners and a plurality of CO sensors disposed therein. The computer storage medium includes code for receiving a plurality of signals from the plurality of CO sensors disposed at a first plurality of locations in the boiler system. The computer storage medium further includes code for determining a plurality of CO levels at the first plurality of locations based on the plurality of signals. The computer storage medium further includes code for determining a second plurality of locations that have CO levels greater than or equal to a threshold CO level. The second plurality of locations is a subset of the first plurality of locations. The computer storage medium further includes code for determining a second plurality of burners in the boiler system that are contributing to the second plurality of locations having CO levels greater than or equal to the threshold CO level. The second plurality of burners is a subset of the first plurality of burners. The computer storage medium further includes code for determining an amount of CO being generated by each burner of the first plurality of burners for each location of the second plurality of locations. The computer storage medium further includes code for increasing an A/F ratio of at least one burner of the second plurality of burners to increase A/F ratios at the second plurality of locations in order to decrease the CO levels at the second plurality of locations toward the threshold CO level, based on the amount of CO being generated by the at least one burner of the second plurality of burners. 
   Other systems and/or methods according to the embodiments will become or are apparent to one with skill in the art upon review of the following drawings and detailed description. It is intended that all such additional systems and methods be within the scope of the present invention, and be protected by the accompanying claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates a power generation system having a boiler system and a control system in accordance with an exemplary embodiment; 
       FIG. 2  is a block diagram of software algorithms utilized in the control system of  FIG. 1 ; 
       FIGS. 3-5  are flowcharts of a method for adjusting CO levels in predetermined locations of the boiler system of  FIG. 1 ; 
       FIG. 6  is a schematic of mapped values utilized by the control system of  FIG. 1  for controlling burner A/F ratio values based on CO levels in the boiler system; and 
       FIG. 7  is a schematic of a burner utilized in the boiler system of  FIG. 1 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIG. 1 , a power generation system  10  for generating electrical power is illustrated. The power generation system  10  includes a boiler system  12 , a control system  13 , a turbine generator  14 , a conveyor  16 , a silo  18 , a coal feeder  20 , a coal pulverizer  22 , an air source  24 , and a smokestack  28 . 
   The boiler system  12  is provided to burn an air-coal mixture to heat water to generate steam therefrom. The steam is utilized to drive the turbine generator  14 , which generates electricity. It should be noted that in an alternative embodiment, the boiler system  12  could utilize other types of fuels, instead of coal, to heat water to generate steam therefrom. For example, the boiler system  12  could utilize any conventional type of hydrocarbon fuel such as gasoline, diesel fuel, oil, natural gas, propane, or the like. The boiler system  12  includes a furnace  40  coupled to a back path portion  42 , an air intake manifold  44 , burners  47 ,  48 ,  50 ,  52 , an air port  53 , and conduits  59 ,  60 ,  62 ,  64 ,  66 ,  68 . 
   The furnace  40  defines a region where the air-coal mixture is burned and steam is generated. The back path portion  42  is coupled to the furnace  40  and receives exhaust gases from the furnace  40 . The back pass portion  42  transfers the exhaust gases from the furnace  40  to the smokestack  28 . 
   The air intake manifold  44  is coupled to the furnace  40  and provides a predetermined amount of secondary air to the burners  47 ,  48 ,  50 ,  52  and air port  53  utilizing the throttle valves  45 ,  46 . Further, the burners  47 ,  48 ,  50 ,  52  receive an air-coal mixture from the air source  24  via the conduits  60 ,  62 ,  64 ,  66 , respectively. The burners  47 ,  48 ,  50 ,  52  and air port  53  are disposed through apertures in the furnace  40 . The burners  47 ,  48 ,  50 ,  52  emit flames into an interior region of the furnace  40  to heat water. Because the burners  47 ,  48 ,  50 ,  52  have a substantially similar structure, only a detailed explanation of the structure of the burner  47  will be provided. Referring to  FIG. 7 , the burner  47  has concentrically disposed tubes  70 ,  72 ,  74 . The tube  70  receives the primary air-coal mixture (air-fuel mixture)from the conduit  60 . The conduit  72  is disposed around the conduit  70  and receives secondary air from the air intake manifold  44 . The conduit  74  is disposed around the conduit  72  and receives tertiary air also from the air intake manifold  44 . The total air-coal mixture supplied to the burner  47  is ignited at an outlet port of the burner  47  and burned in the furnace. The burner  47  further includes a valve  75  disposed in the flow path between the tube  70  and the tube  72 . An operational position of the valve  75  can be operably controlled by the controller  122  to control an amount of tertiary air being received by the burner  47 . Further, the burner  47  further includes a valve  77  disposed in the flow path between the tube  72  and the tube  74 . An operational position of the valve  77  can be operably controlled by the controller  122  to control an amount of secondary air being received by the burner  47 . 
   Referring to  FIG. 1 , the control system  13  is provided to control an amount of air and coal received by the burners  47 ,  48 ,  50 ,  52  and air received by the air port  53 . In particular, the control system  13  is provided to control A/F ratios and air-fuel mass flows at the burners  47 ,  48 ,  50 ,  52  and air injection port  53  to control CO levels, temperature levels, and a rate of slag formation at predetermined locations in the boiler system  12 . The control system  13  includes electrically controlled primary air and coil valves  80 ,  82 ,  84 ,  86 ,  88 , a combustion air actuator  90 , an overfire air actuator  92 , CO sensors  94 ,  96 ,  98 ,  99 , temperature sensors  110 ,  112 ,  114 ,  115 , slag detection sensors  116 ,  118 ,  120 ,  121 , mass air flow sensors  117 ,  119 , a coal flow sensor  123 , and a controller  122 . It should be noted that for purposes of discussion, it is presumed that the CO sensor  94 , the temperature sensor  110 , and the slag detection sensor  116  are disposed substantially at a first location within the boiler system  12 . Further, the CO sensor  96 , the temperature sensor  112 , the slag detection sensor  118  are disposed substantially at a second location within the boiler system  12 . Further, the CO sensor  98 , the temperature sensor  114 , the slag detection sensor  120  are disposed substantially at a third location within the boiler system  12 . Still further, the CO sensor  99 , the temperature sensor  115 , and the slag detection sensor  121  are disposed substantially at a fourth location with the boiler system  12 . Of course, it should be noted that in alternative embodiments the CO sensors, temperature sensors, and slag detection sensors can be disposed in different locations with respect to one another. Further, in an alternate embodiment, the CO sensors  94 ,  96 ,  98 ,  99  are disposed away from the first, second, third, and fourth locations respectively in the boiler system  12  and the CO levels at the first, second, third and fourth locations are estimated from the signals of CO sensors  94 ,  96 ,  98 ,  99 , respectively, utilizing computational fluid dynamic techniques known to those skilled in the art. Further, in an alternate embodiment, the temperature sensors  110 ,  112 ,  114 ,  115  are disposed away from the first, second, third, and fourth locations, respectively, and the temperature levels at the first, second, third, and fourth locations are estimated from the signals of temperature sensors  110 ,  112 ,  114 ,  115 , respectively utilizing computational fluid dynamic techniques known to those skilled in the art. Further, in an alternate embodiment, the slag detection sensors  116 ,  118 ,  120 ,  121  are disposed away from the first, second, third, and fourth locations, respectively, and the slag thickness levels are estimated from the signals of the slag detection sensors  116 ,  118 ,  120 ,  121 , respectively, utilizing computational fluid dynamic techniques known to those skilled in the art. 
   The electrically controlled valves  80 ,  82 ,  84 ,  86 ,  88  are provided to control an amount of primary air or transport air delivered to the burners  47 ,  48 ,  50 ,  52  and conduit  68 , respectively, in response to control signals (FV 1 ), (FV 2 ), (FV 3 ), (FV 4 ), (FV 5 ), respectively, received from the controller  122 . The primary air carries coal particles to the burners. 
   The actuator  90  is provided to control an operational position of the throttle valve  45  in the air intake manifold  44  for adjusting an amount of combustion air provided to the burners  47 ,  48 ,  50 ,  52 , in response to a control signal (AV 1 ) received from the controller  122 . 
   The actuator  92  is provided to control an operational position of the throttle valve  46  for adjusting an amount of over-fire air provided to the air port  53 , in response to a control signal (AV 2 ) received from the controller  122 . 
   The CO sensors  94 ,  96 ,  98 ,  99  are provided to generate signals (C 01 ), (C 02 ), (C 03 ), (C 04 ) indicative of CO levels at the first, second, third, and fourth locations, respectively, within the boiler system  12 . It should be noted that in an alternative embodiment, the number of CO sensors within the boiler system  12  can be greater than four CO sensors. For example, in an alternative embodiment, a bank of CO sensors can be disposed within the boiler system  12 . As shown, the CO sensors  94 ,  96 ,  98 ,  99  are disposed in the back pass portion  42  of the boiler system  12 . It should be noted that in an alternative embodiment, the CO sensors can be disposed in a plurality of other positions within the boiler system  12 . For example, the CO sensors can be disposed at an exit plane of the boiler system  12 . 
   The temperature sensors  110 ,  112 ,  114 ,  115  are provided to generate signals (TEMP 1 ), (TEMP 2 ), (TEMP 3 ), (TEMP 4 ) indicative of temperature levels at the first, second, third and fourth locations, respectively, within the boiler system  12 . It should be noted that in an alternative embodiment, the number of temperature sensors within the boiler system  12  can be greater than four temperature sensors. For example, in an alternative embodiment, a bank of temperature sensors can be disposed within the boiler system  12 . As shown, the temperature sensors  110 ,  112 ,  114 ,  115  are disposed in the furnace exit plane portion  42  of the boiler system  12 . It should be noted that in an alternative embodiment, the temperature sensors can be disposed in a plurality of other positions within the boiler system  12 . For example, the temperature sensors can be disposed at an exit plane of the boiler system  12 . 
   The slag detection sensors  116 ,  118 ,  120 ,  121  are provided to generate signals (SLAG 1 ), (SLAG 2 ), (SLAG 3 ), (SLAG 4 ) indicative of slag thicknesses at the first, second, third, and fourth locations, respectively, within the boiler system  12 . It should be noted that in an alternative embodiment, the number of slag detection sensors within the boiler system  12  can be greater than four slag detection sensors. For example, in an alternative embodiment, a bank of slag detection sensors can be disposed within the boiler system  12 . As shown, the slag detection sensors  116 ,  118 ,  120 ,  121  are disposed in the back path portion  42  of the boiler system  12 . It should be noted that in an alternative embodiment, the slag detection sensors can be disposed in a plurality of other positions within the boiler system  12 . For example, the slag detection sensors can be disposed at an exit plane of the boiler system  12 . 
   The mass flow sensor  119  is provided to generate a (MAF 1 ) signal indicative of an amount of primary air being supplied to the conduit  59 , that is received by the controller  122 . 
   The mass flow sensor  117  is provided to generate a (MAF 2 ) signal indicative of an amount of combustion air being supplied to the intake manifold  44  and the burners and air ports, that is received by the controller  122 . 
   The coal flow sensor  123  is provided to generate a (CF) signal indicative of an amount of coal being supplied to the conduit  59 , that is received by the controller  122 . 
   The controller  122  is provided to generate control signals to control operational positions of the valves  80 ,  82 ,  84 ,  86 ,  88  and actuators  90 ,  92  for obtaining a desired A/F ratio at the burners  47 ,  48 ,  50 ,  52 . Further, the controller  122  is provided to receive signals (CO 1 -CO 4 ) from the CO sensors  94 ,  96 ,  98 ,  99  indicative of CO levels at the first, second, third and fourth locations and to determine the CO levels therefrom. Further, the controller  122  is provided to receive signals (TEMP 1 -TEMP 4 ) from the temperature sensors  110 ,  112 ,  114 ,  115  indicative of temperature levels at the first, second, third, and fourth locations and to determine temperature levels therefrom. Still further, the controller  122  is provided to receive signals (SLAG 1 -SLAG 4 ) from the slag detection sensors  116 ,  118 ,  120 ,  121  indicative of slag thicknesses at the first, second, third, and fourth locations and to determine slag thicknesses therefrom. The controller  122  includes a central processing unit (CPU)  130 , a read-only memory (ROM)  132 , a random access memory (RAM)  134 , and an input-output (I/O) interface  136 . Of course any other conventional types of computer storage media could be utilized including flash memory or the like, for example. The CPU  30  executes the software algorithms stored in at least one of the ROM  132  and the RAM  134  for implementing the control methodology described below. 
   Referring to  FIG. 2 , a block diagram of the software algorithms executed by the controller  122  is illustrated. In particular, the software algorithms include a burner A/F ratio estimation module  140 , a spatial A/F ratio estimation module  142 , a mass flow based influence factor map  144 , and a spatial CO estimation module  146 . 
   The burner A/F ratio estimation module  140  is provided to calculate an A/F ratio at each of the burners  47 ,  48 ,  50 ,  52 . In particular, the module  140  calculates the A/F ratio and each of the burners based upon the amount of primary air, secondary air, and tertiary air and coal being provided to be burners  47 ,  48 ,  50 ,  52  and an amount of coal being provided by the coal pulverizer  22 . 
   The mass flow based influence factor map  144  comprises a table that correlates a mass flow amount of exhaust gases from each burner to each of the first, second, third, and fourth locations within the boiler system  12 . The controller  122  can utilize the mass flow based influence factor map  144  to determine which burners are primarily affecting particular locations within the boiler system  12 . In particular, the controller  122  can determine that a particular burner is primarily affecting a particular location within the boiler system  12  by determining that a mass flow value from the particular burner to the particular location is greater than a threshold mass flow value. 
   In an alternative embodiment, the mass flow based influence factor map  144  comprises a table that indicates a percentage value indicating a percentage of the mass flow from each burner that flows to each of the first, second, third, and fourth locations. The controller  122  can determine that a particular burner is primarily affecting a particular location within the boiler system  12  by determining that a percentage value associated with a particular burner and a particular location is greater than a threshold percentage value. For example, the table could indicate that 10% of the mass flow at the first location is from the burner  47 . If the threshold percentage value is 5%, then the controller  122  would determine burner  47  is primarily affecting the mass flow at the first location. 
   The mass flow based influence factor map  144  can be determined using isothermal physical models and fluid dynamic scaling techniques of the boiler system  12  or computational fluid dynamic models of the boiler system  12 . 
   The spatial A/F ratio estimation model  142  is provided to calculate an A/F ratio at each of the first, second, third, and fourth locations in the boiler system  12 . In particular, the module  142  utilizes the A/F ratios associated with each of the burners and the mass flow based influence factor map  144  to calculate an A/F ratio at each of the first, second, third, and fourth locations in the boiler system  12 . 
   The spatial CO estimation model  142  is provided to calculate a CO level at each of the first, second, third, and fourth locations in the boiler system  12 . In particular, the module  142  utilizes the A/F ratio at each of the first, second, third, and fourth locations to estimate the CO levels at the first, second, third, and fourth locations. 
   Referring to  FIGS. 3-5 , a method for adjusting CO levels in the boiler system  12  will now be explained. The method can be implemented utilizing software algorithms executed by the controller  122 . 
   At step  150 , a first plurality of CO sensors disposed at a first plurality of locations, respectively, in a boiler system  12  generate a first plurality of signals, respectively, indicative of CO levels at the first plurality of locations. For example, the CO sensors  94 ,  96 ,  98 ,  99  can generate signals (CO 1 ), (C 02 ), (C 03 ), (C 04 ) respectively, indicative of CO levels at the first, second, third, and fourth locations, respectively. 
   At step  152 , the controller  122  receives the first plurality of signals and determines a first plurality of CO levels associated with the first plurality of locations. For example, the controller  122  can receive the signals (CO 1 ), (C 02 ), (C 03 ), (C 04 ) and determine CO levels associated with the first, second, third, and fourth locations, respectively. 
   At step  154 , the controller  122  determines a second plurality of locations comprising a subset of the first plurality of locations, that have CO levels greater than or equal to a threshold CO level. For example, the controller  122  can determine that the first and second locations have CO levels greater than or equal to the threshold CO level. 
   At step  156 , the controller  122  determines a third plurality of locations comprising a subset of the first plurality of locations, that have CO levels less than the threshold CO level. For example, the controller  122  can determine that the third and fourth locations have CO levels less than the threshold CO level. 
   At step  158 , the air flow sensor  119  generates the (MAFI) signal indicative of a primary air mass flow entering the boiler system  12 , that is received by the controller  122 . 
   At step  159 , the air flow sensor  117  generates the (MAF 2 ) signal indicative of a combustion air mass flow entering the intake manifold  44 , that is received by the controller. The combustion air mass flow comprises the secondary air and tertiary air received by the burners and the overfire air received by the air port  53 . 
   At step  160 , the coal flow sensor  123  generates the (CF) signal indicative of an amount of coal (e.g., total mill coal flow) entering the boiler system  12 , that is received by the controller  122 . Of course, in an alternate embodiment, the amount of coal being received by each burner can be calculated or monitored using coal flow sensors. 
   At step  162 , the controller  122  executes the burner A/F ratio calculation module  140  to determine an A/F ratio of each of the first plurality of burners in the boiler system  122  based on the (MAFI) signal, the (MAF 2 ) signal, and the (CF) signal. For example, the controller  122  can execute the burner A/F ratio calculation module  140  to determine A/F ratios for the burners  47 ,  48 ,  50 ,  52  based on the (MAFI) signal, the (MAF 2 ) signal, and the (CF) signal. After step  162 , the controller  122  substantially simultaneously executes both sets of steps  164 - 168  and steps  170 - 174 . 
   Referring to  FIG. 4 , the steps  164 - 168  will now be explained. At step  164 , the controller  122  executes the spatial A/F ratio estimation module  142  that utilizes a mass flow based influence factor map  144 , to determine an A/F ratio at each of the second plurality of locations, based on the A/F ratio at each of the first plurality of burners, and to determine a second plurality of burners comprising a subset of the first plurality of burners that are primarily influencing the CO levels at the second plurality of locations. For example, the controller  122  can execute the module  142  the utilizes the mass flow based influence factor map  144  to determine A/F ratios at the first and second locations, based on the A/F ratio at each of the burners  47 ,  48 ,  50 ,  52 . Further, for example, the controller  122  can determine that the burners  47 ,  48  are primarily influencing the CO levels at the first and second locations in the boiler system  12 . After step  164 , the method advances to step  166 . 
   At step  166 , the controller  122  executes a spatial CO estimation module  146  to estimate an amount of CO being generated by each of the first plurality of burners at each of the second plurality of locations in the boiler system  12 . For example, the controller  122  can execute the module  146  to estimate an amount of CO being generated by the burners  47 ,  48 ,  50 ,  52  at the first and second locations in the boiler system  12 . After step  166 , the method advances to step  168 . 
   At step  168 , the controller  122  increases an A/F ratio of at least one burner of the second plurality of burners, based on the amount of CO being generated by at least one burner of the second plurality burners, to adjust the CO levels at the second plurality of locations toward the threshold CO level. For example, the controller  122  can increase an A/F ratio of at least one of the burners  47 ,  48 , based on the amount of CO being generated by at least one of burners  47 ,  48 , to adjust CO levels at first and second locations toward the threshold CO level by increasing a fuel mass-flow into at least one of burners  47 ,  48  while maintaining or decreasing an air mass-flow to the at least one of burners  47 ,  48 . Referring to  FIG. 6 , the controller  122  can utilize a table or transfer function illustrated by the waveform  180  to determine a desired A/F ratio or an A/F ratio adjustment value for the burners  47 ,  48  based on a measured CO level. After step  168 , the method returns to step  150 . 
   Referring to  FIG. 5 , the steps  170 - 174  will now be explained. At step  170 , the controller  122  executes the spatial A/F ratio estimation module  142  that utilizes the mass-flow based influence factor map  144 , to determine an A/F ratio at each of the third plurality of locations, based on the A/F ratio at each of the first plurality of burners, and to determine a third plurality of burners comprising a subset of the first plurality of burners that are primarily influencing the CO levels at the third plurality of locations. For example, the controller  122  can execute the module  142  the utilizes the mass flow based influence factor map  144  to determine A/F ratios at the third and fourth locations, based on the A/F ratio at each of the burners  47 ,  48 ,  50 ,  52 . Further, for example, the controller  122  can determine that the burners  50 ,  52  are primarily influencing the CO levels at the third and fourth locations in the boiler system  12 . After step  170 , the method advances to step  172 . 
   At step  172 , the controller executes the spatial CO estimation module  146  to estimate an amount of CO being generated by each of the first plurality of burners at each of the third plurality of locations in the boiler system  12 . For example, the controller  122  can execute the module  146  to estimate an amount of CO being generated by the burners  47 ,  48 ,  50 ,  52  at the third and fourth locations in the boiler system  12 . After step  172 , the method advances to step  174 . 
   At step  174 , the controller  122  decreases an A/F ratio of at least one burner of the third plurality of burners, based on the amount of CO being generated by at least one burner of the third plurality burners, while maintaining CO levels at the third plurality of locations less than or equal to the threshold CO level. For example, the controller  122  can decrease an A/F ratio of at least one of the burners  50 ,  52 , based on the amount of CO being generated by at least one of burners  50 ,  52 , while maintaining CO levels at the third and fourth locations less than or equal to the threshold CO level by increasing a fuel mass-flow into at least one of the burners  50 ,  52  while maintaining or decreasing an air mass-flow to the at least one of burners  50 ,  52 . Referring to  FIG. 6 , the controller  122  can utilize a table or transfer function illustrated by the waveform  180  to determine a desired A/F ratio or an A/F ratio adjustment value for the burners  50 ,  52  based on a measured CO level. After step  174 , the method returns to step  150 . 
   The inventive system, method, and article of manufacture for adjusting CO levels provide a substantial advantage over other system and methods. In particular, these embodiments provide a technical effect of adjusting A/F ratios at burners to decrease CO levels at predetermined locations in a boiler system that are greater than a threshold CO level to improve outputted CO emission levels. 
   The above-described methods can be embodied in the form of computer program code containing instructions embodied in tangible media, such as floppy diskettes, CD ROMs, hard drives, or any other computer-readable storage medium, wherein, when the computer program code is loaded into and executed by a computer, the computer becomes an apparatus for practicing the invention. 
   While the invention is described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalence may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to the teachings of the invention to adapt to a particular situation without departing from the scope thereof. Therefore, it is intended that the invention not be limited to the embodiment disclosed for carrying out this invention, but that the invention includes all embodiments falling with the scope of the intended claims. Moreover, the use of the term&#39;s first, second, etc. does not denote any order of importance, but rather the term&#39;s first, second, etc. are used to distinguish one element from another.