Abstract:
An oxygen measuring apparatus ( 500 ) includes an inlet pipe ( 506 ) having a first end and a second end, an oxygen sensor ( 511 ) arranged inside the inlet pipe ( 506 ) between the first end of the inlet pipe and the second end of the inlet pipe, the oxygen sensor ( 511 ) having a communication medium ( 515 ) disposed thereon and extending through the second end of the inlet pipe ( 506 ), a filtering medium arranged ( 505 ) inside the inlet pipe between the oxygen sensor ( 511 ) and the first end of the inlet pipe, a housing ( 501 ) arranged against the second end of the inlet pipe, and a sensor control interface ( 512 ) arranged within the housing ( 501 ) and in communication with the communication medium ( 515 ) of the oxygen sensor ( 511 ).

Description:
FIELD OF INVENTION 
     The subject matter disclosed herein relates generally to the field of oxygen measurement, and more particularly to oxygen measurement in combustion control applications. 
     DESCRIPTION OF RELATED ART 
     In order to properly operate a boiler, it may be necessary to control a fuel/air ratio, boiler water level, and steam pressure/temperature of the boiler. Generally, there may be several actuators involved in control of these variables. 
     Conventionally, the fuel/air ratio is controlled throughout the entire operating range of the boiler to ensure boiler safety and combustion efficiency. Fuel/air ratio control is implemented through a coordinated mapping between fuel valve position and air damper position within a firing range of the boiler. If the coordinated relationship between the actuators is fixed through a mechanical system, then the combustion system is called a linkage combustion system. If the actuator positions are flexible and independently adjustable in response to process conditions (e.g. steam pressure/flow, or water temperature) then the combustion system may be a parallel positioning system (if without flow sensors for fuel/air ratio control) or a fully-metered system with installed fuel and air flow sensors for fuel/air ratio control. 
     BRIEF SUMMARY 
     According to one aspect of the invention, an oxygen measuring apparatus includes an inlet pipe having a first end and a second end, an oxygen sensor arranged inside the inlet pipe between the first end of the inlet pipe and the second end of the inlet pipe, the oxygen sensor having a communication medium disposed thereon and extending through the second end of the inlet pipe, a filtering medium arranged inside the inlet pipe between the oxygen sensor and the first end of the inlet pipe, a housing arranged against the second end of the inlet pipe, and a sensor control interface arranged within the housing and in communication with the communication medium of the oxygen sensor. 
     According to another aspect of the invention, an oxygen measuring apparatus includes an inlet pipe having a first end and a second end, an oxygen sensing cartridge arranged inside the inlet pipe, the oxygen sensing cartridge having an outer wall in contact with an inner wall of the inlet pipe, a first end in contact with the second end of the inlet pipe, a communication medium disposed thereon, and a filtering medium arranged therein, a housing arranged between the second end of the inlet pipe and the first end of the oxygen sensing cartridge, and a sensor control interface arranged within the housing and in communication with the communication medium of the oxygen sensing cartridge. 
     According to another aspect of the invention, a boiler control system includes a combustion chamber, a flue stack in communication with the combustion chamber, a closed-loop boiler control portion in communication with the flue stack and the combustion chamber, and an oxygen measuring apparatus arranged on the flue stack. The oxygen measuring apparatus includes an inlet pipe having a first end and a second end, the inlet pipe extending through a wall of the flue stack, an oxygen sensing cartridge arranged inside the inlet pipe, the oxygen sensing cartridge having an outer wall in contact with an inner wall of the inlet pipe, a first end in contact with the second end of the inlet pipe and the wall of the flue stack, a communication medium disposed thereon, and a filtering medium arranged therein, a housing arranged around the second end of the inlet pipe, the first end of the oxygen sensing cartridge, and against the wall of the flue stack, and a sensor control interface arranged within the housing and in communication with the communication medium of the oxygen sensing cartridge. 
     Other aspects, features, and techniques of the invention will become more apparent from the following description taken in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       Referring now to the drawings wherein like elements are numbered alike in the several FIGURES: 
         FIG. 1  depicts a boiler system with fuel and air flow control; 
         FIG. 2  depicts a parallel positioning closed-loop boiler control method, according to an example embodiment; 
         FIG. 3  depicts a graph of oxygen levels in a boiler; 
         FIG. 4  depicts parallel positioning closed-loop boiler control method with oxygen trim, according to an example embodiment; 
         FIG. 5  depicts an oxygen measuring apparatus, according to an example embodiment; 
         FIG. 6  depicts an oxygen measuring apparatus, according to an example embodiment; 
         FIG. 7  depicts an oxygen measuring apparatus, according to an example embodiment; 
         FIG. 8  depicts an oxygen probe portion of an oxygen measuring apparatus, according to an example embodiment; 
         FIG. 9  depicts an oxygen measuring apparatus, according to an example embodiment; 
         FIG. 10  depicts a control system of an oxygen measuring apparatus, according to an example embodiment; and 
         FIG. 11  depicts a control system of an oxygen measuring apparatus, according to an example embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of an oxygen measuring apparatus and control system are provided herein, with example embodiments being discussed below in detail. 
     As described herein, example embodiments provide a modular, low cost oxygen measuring apparatus that is relatively easy to maintain; relatively easy to calibrate, includes capability of monitoring/data acquisition, and has both digital and analog means of communications with subsystems and control systems. 
     Example embodiments may include a wideband Universal Exhaust Gas Oxygen (UEGO) Sensor/probe for use in monitoring oxygen concentration in combustion gas mixtures. The UEGO probe may be any suitable probe. For example, suitable probes may include oxygen monitoring probes typically used in automotive applications for emissions control. The UEGO probe control electronics may be responsible for exciting the oxygen sensor&#39;s heater to a suitable working temperature; responsible for monitoring the operating conditions of the oxygen sensor; and acquiring the sensor&#39;s O2 level signal for processing. The processed signal is subsequently provided to a control system as part of a feedback signal for a closed loop system, and/or provided to other suitable components for monitoring. 
     Example embodiments are capable of monitoring stack temperature of a boiler via a thermocouple or other suitable temperature measuring apparatus. Acquired temperature data may be used to derive combustion efficiency data, and/or for other purposes. Communication with the UEGO probe may be facilitated over a communications medium (e.g., Serial, CAN bus, modbus, etc) or as an analog voltage/current signal. 
     Hereinafter, example embodiments are described in detail. 
       FIG. 1  depicts a boiler system. As illustrated, the system  100  includes a furnace/combustion chamber  101 , a load  102  arranged on the boiler, and a stack  103  arranged on the load. The system  100  further includes a boiler control portion  104  in communication with the stack  103 , the load  102 , and the furnace/combustion chamber  101 . 
     Stack temperature and oxygen information (e.g., from an oxygen measuring apparatus) may be provided to the boiler control portion  104  over a communication medium (e.g., Serial, CAN bus, etc), as a voltage/current signal, or as any suitable signal/data. Steam pressure information may be provided to the boiler control portion  104  over any suitable medium as described above. In response to the temperature, oxygen, and steam pressure information, the boiler control portion  104  may control fuel and air to maintain stable and/or efficient operation of the boiler system  100 . 
     For example, the system  100  includes air driving fan  107  in communication with variable speed drive  106 , which is in further communication with the boiler control portion  104 . The system  100  further includes oxygen trim servo  105  in communication with the boiler control portion  104 . The oxygen trim servo  105  may be arranged between the air driving fan  107  and the furnace/combustion chamber  101  such that air driven by the fan  107  may be forced through the servo  105  into the furnace/combustion chamber  101 . Thus, the boiler control portion  104  may accurately control a level of oxygen and air entering the furnace/combustion chamber  101 . 
     The system  100  further includes fuel oil control servo  108  and fuel gas control servos  109  in communication with the boiler control portion  104 . The control servos  108 - 109  control the flow of fuel oil and fuel gas, respectively, entering the furnace/combustion chamber  101 . Thus, the boiler control portion  104  may accurately control the flow of fuel oil or fuel gas entering the furnace/combustion chamber  101 . 
     According to example embodiments, boiler control portions of boiler systems may include closed-loop boiler control models to accurately maintain operation of boiler systems and their efficiency. 
       FIG. 2  depicts a parallel positioning closed-loop boiler control method, according to an example embodiment. As illustrated, the method  200  includes receiving a pressure value P sp  of a boiler, and mixing the measured value with a calculated value at block  201 . The mixed value is used to determine a firing rate through function K at block  202 . Thereafter, a fuel/air servo mapping function f(x) is applied to the firing rate at block  203 . The fuel/air servo map function  203  is determined over a boiler firing rate range during a commissioning process. 
     Outputs of the function f(x) are applied to transfer functions G a  and G f  at blocks  204  and  205 , respectively. Subsequently, outputs of the transfer functions G a  and G f  are applied to boiler transfer function G at block  206 . Outputs of the boiler transfer function G and an external disturbance transfer function G d  ( 208 ) are mixed at  207  to determine the calculated value described with reference to block  201 . Thus, boiler control method  200  is a closed loop control method. 
     Because the control system  200  does not include mass flow sensors for measuring air flow and fuel flow, flow through air and fuel servos may not be accurately controlled. Any changes in air or fuel, such as air density, temperature, humidity, or fuel supplied pressure, result in mass flow changes in air side or fuel side and fuel/air ratio will deviate from the fuel/air servo map generated at mapping function f(x) ( 203 ). This will cause variations in excess air levels. In order to prevent the excess air level from going too low which may cause unsafe boiler operation, the fuel/air servo map function should be defined such that there is enough excess air during the combustion process. However, too much excess air will result in lower combustion efficiency.  FIG. 3  depicts excess oxygen curves compared to firing rates in graph  300 . Generally, it may be necessary to have increased excess oxygen in lower firing rates compared with higher firing rates. This is mainly due to flame instability issues in the lower firing range. If there is no oxygen trim control, the oxygen curve could be between the maximum oxygen curve and the minimum oxygen curve of  FIG. 3 . 
     In order to obtain better combustion efficiency over a relatively long period of time, mass flow variations may be better addressed using oxygen trim control. This may be facilitated through control of the excess air/oxygen in a more precise manner. For example, in order to close the loop for oxygen trim, an oxygen sensor is needed to measure the excess air in the stack. 
       FIG. 4  depicts parallel positioning closed-loop boiler control method with oxygen trim, according to an example embodiment. As illustrated, the method  400  includes receiving a pressure value P sp  of a boiler, and mixing the measured value with a calculated value at block  401 . The mixed value is used to determine a firing rate through function K at block  402 . Thereafter, a fuel/air servo mapping function f(x) is applied to the firing rate and a mixed oxygen trim level ( 406 ) at block  407 . 
     Outputs of the function f(x) are applied to transfer functions G a  and G f  at blocks  408  and  409 , respectively. Subsequently, outputs of the transfer functions G a  and G f  are applied to boiler transfer function G at block  410 . Outputs of the boiler transfer function G and an external disturbance transfer function G d  ( 412 ) are mixed at  411  to determine the calculated value described with reference to block  401 . 
     Regarding the oxygen trim level, the firing rate calculated through function K is applied to a target excess oxygen curve at block  403 . Subsequently, the applied curve is mixed with an oxygen output value from the boiler transfer function G at block  404 . The mixed value is applied to oxygen trim transfer function K 2  at block  405 , and mixed with the firing rate at block  406 , as described above. Thus, boiler control method  400  is a closed loop control method. 
     As described above, in order to trim oxygen in a boiler system more effectively, an oxygen measuring sensor or apparatus is necessary. 
       FIG. 5  depicts an oxygen measuring apparatus, according to an example embodiment. As illustrated, the apparatus  500  includes housing  501 . The housing  501  may be any suitable housing, including high-temperature resistant plastic, metal (e.g., aluminum), or any suitable material. The apparatus  500  further includes tubing  502  arranged within the housing  501 . The tubing  502  may be any suitable tubing, including metal or aluminum tubing. The apparatus  500  further includes thermal gasket  503  disposed to seal tubing  502  within the housing  501  and against tubing  504 . Tubing  504  may be any suitable tubing, for example, stainless steel, aluminum, or metal tubing. As illustrated, the tubing  504  may extend beyond the housing  501  and may curve or bend against tubing/pipe  506  to facilitate measurement of gases within a flue stack. For example, pipe  506  may extend into a flue stack and allow flue gases to enter one end, flow through filter  505 , and be measured for oxygen content at sensor  511 . 
     The filter  505  is arranged within the tubing  504 , and disposed to filter gases entering the housing  501 . The filter  505  may be any suitable filter, including mesh or micron filters. The filter  505  may be supported within the tubing  504  with screws, bolts, or any other suitable attachment means  507 . The apparatus  500  further includes thermal break  508  disposed between an oxygen sensor  511  within the tubing  504  and the tubing  502 . The thermal break  508  may be formed of any suitable material, including machinable ceramic, glass, or other suitable material. 
     The apparatus  500  further includes supporting rod(s)  510  disposed to support the thermal break  509  and the tubing  502  against an interior wall of the housing  501 . A thermocouple and/or oxygen communication interface  512  is further included within the housing  501 , which is in communication with a thermocouple and/or the oxygen sensor  511 . 
       FIG. 6  depicts a perspective view of the oxygen measuring apparatus  500  and  FIG. 7  depicts an alternate perspective view of the oxygen measuring apparatus  500 . The housing  501  is depicted as translucent in  FIG. 7  for illustrative purposes, although a translucent/transparent high-temperature resistant plastic may be used for the housing  501 . As illustrated in  FIG. 7 , thermo couple  514  is arranged on tubing/pipe  504 / 506  using supportive means  516 . The supportive means  516  may be support portions welded, glued, or otherwise affixed to the tubing/pipe  504 / 506 . Also, although described as a thermocouple, it should be understood that any suitable temperature measuring probe/apparatus may be used. As further illustrated, flue gas outlets  512 - 513  are arranged on the tubing/pipe  504 / 506 . The flue gas outlets  512 - 513  may penetrate walls of the tubing/pipe  504 / 506  and be disposed to release a portion of flue gases entering the pipe  506  from a flue stack. In this manner, a relatively continuous sample of flue gases may flow through the filter  505  and be exposed against a sampling portion of the sensor  511 . In order to further illustrate example embodiments, a detailed view of an oxygen probe portion/cartridge of the apparatus  500  is provided in  FIG. 8 . 
       FIG. 8  depicts an oxygen probe portion  520  of an oxygen measuring apparatus, according to an example embodiment. As illustrated, the probe  511  may be arranged within the portion  520  using attachment/supportive means  517 . The means  517  may be nuts, bolts, spacers, or other supportive means. Furthermore, a gasket or sealing ring  518  may further support the probe  511  within the portion  520 . The portion  520  may be entirely or partially arranged within the tubing  506  of the apparatus  500 . Further, a communication medium  515  may extend from the oxygen probe  511  to an interior of the housing  501 . The communication medium  515  may be connectable to the probe  511  and the communication portion/interface  512  described above. Alternatively, the communication medium  515  may be permanently affixed to the probe  511  (e.g., welded or soldered wire). The entire oxygen measuring portion  520  may be arranged as a replaceable cartridge to facilitate easy maintenance and calibration of the apparatus  500 . Furthermore, as illustrated, the portion  520  may include an outer wall disposed to be in contact with an inner wall of the pipe  506 . 
       FIG. 9  depicts the oxygen measuring apparatus  500  arranged on a flue stack wall  521 . As shown, the housing  501  may be arranged against the wall  521  while the tubing/pipe  504 / 506  extends into the flue stack. In this manner, the housing  501  may protect the communications interface  512 , while the oxygen measuring portion  520  may remain within the flue stack, thereby facilitating measurement of oxygen within the flue gases. 
       FIG. 10  depicts a control system of an oxygen measuring apparatus, according to an example embodiment. The system  1000  includes the communications interface  512  in communication with an oxygen sensor  1003 . The oxygen sensor  1003  may be somewhat similar to the oxygen sensor  511  described above. The interface  512  may include a sensor control portion  1022 , storage portion  1023 , a power supply  1024 , and a calibration portion  1025 . The sensor control portion  1022  may be a control portion disposed to provide control for sensor temperature, filter and condition signals from the sensor, and monitor health of the sensor. For example, in order to operate correctly, the sensor  1003  may need to be at a correct operating temperature. Furthermore, communication with the probe to retrieve oxygen information and monitor health is necessary. Thus, the sensor control portion  1022  may determine necessary parameters and provide/receive necessary signals over medium  1020 . For example, medium  1020  may be somewhat similar to medium  515  described above. The interface  512  may be in further communication with thermocouple  1004  over medium  1021 . For example, medium  1021  may be comprised of distinct metals which are welded at the thermo couple  1004  to retrieve a voltage indicative of temperature at the weld. Alternatively, medium  1021  may be a medium disposed to communication with any other temperature sensor, for example, a high-temperature resistant sensor capable of monitoring temperatures within a flue stack. Thus, the interface  512  may monitor temperature information to facilitate control of the sensor  1003 . 
     Storage portion  1023  may be any suitable electronic storage medium. For example, storage portion  1023  may be non-volatile memory or other suitable computer readable memory. The power supply  1024  may be any suitable power supply, including a battery, plurality of batteries, transformer in communication with an external voltage source, or any other power supply disposed to provide power to the sensor control portion  1022 , storage portion  1023 , and the calibration portion  1025 . The calibration portion  1025  may be a manual calibration means, including a switch, knob, button-system, or any other suitable calibration mechanism capable of providing selective control of the sensor  1003  and the thermocouple  1004 . 
     The system  1000  further includes external interface  1001  in communication with the interface  512 . For example, external interface  1001  may be a computer apparatus or processor, configured and disposed to communicate with the interface  512  over communication medium  1010 . According to at least one example embodiment, the external interface  1001  is a dedicated interface disposed to monitor the probe  1003  and the thermo couple  1004  in a dedicated manner. Alternatively, the external interface may also be a programmable computing apparatus or processor disposed to monitor the probe  1003  and the thermocouple  1004  in a programmable manner (e.g., programmable temperature/oxygen control curves, etc). 
       FIG. 11  depicts an alternative control system of an oxygen measuring apparatus, according to an example embodiment. As illustrated, the system  1100  includes an electronic control interface  1101 . The electronic control interface  1101  may include a plurality of control portions. For example, the interface  1101  may include input means  1118 . Input means  1118  may be a plurality of pushbuttons, a keypad, a sequence of knobs, a combination of the same, or any other input means disposed to allow user control of an oxygen measuring apparatus. The interface  1101  may further include display means  1119 . Display means  1119  may be a numerical display, alpha-numerical display, a liquid crystal display, a bank of indicator lights, or any combination of the same. The interface  1101  may further include clock  1120 . Clock  1120  may be a real-time clock or any time-measuring apparatus configured to provide a clock signal for operation of the interface  1101  including log-times or other time information. The interface  1101  may further include storage  1121 . Storage  1121  may be any suitable storage means, for example, as described above with reference to interface  512 . The interface  1101  may further include an internal temperature sensor  1122  configured to monitor the temperature of the actual interface  1101 . The interface  1101  may further include curve and/or peak detection circuit  1123  configured to monitor sensor output to determine when/if a peak in sensor output has occurred. The interface  1101  may further include sensor controller  1124 . The sensor controller  1124  may be somewhat similar to sensor controller  1022  described above. Furthermore, the interface  1101  may include voltage monitor  1125 . 
     Turning back to  FIG. 11 , the system  1100  may also include a power supply  1112  in communication with the interface  1101 . The power supply  1112  may be any suitable power supply capable of providing power to the interface  1101 . 
     The system  1100  may further include oxygen sensor  1116  and thermocouple  1117 . The sensor  1116  and thermocouple  1117  may be somewhat similar to the sensor  1003  and the thermocouple  1004  described above. 
     The system  1100  may further include temperature sensor  1114  in communication with the interface  1101 . For example, the temperature sensor  1114  may be arranged within a housing of an oxygen measuring apparatus. 
     The system  1100  may further include a communication interface  1115 . The communication interface  1115  may be a serial interface, MODBUS interface, or any other suitable interface configured to establish communication between the interface  1101  and any desired external controller/computing apparatus. 
     Furthermore, the system  1100  may include a plurality of signal interfaces  1102 - 1111  configured to provide signals to/from the interface  1101  and a boiler system/external computing apparatus. For example, output signals  1102 - 1105  may provide information about flue stack temperature/oxygen content. Alarm outputs  1106 - 1107  may provide alarm signals associated with burner control. Additionally, inputs  1108 - 1111  may provide inputs to the interface  1101  for external modification/control of the interface  1101 . 
     As describe above, a novel, low-cost oxygen measuring apparatus and associated control systems are provided. The oxygen measuring apparatus may include an oxygen measuring portion or cartridge which is easily replaceable and controlled. Thus, technical benefits include reduced costs associated with maintenance and replacement of oxygen sensors in boiler systems. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. While the description of the present invention has been presented for purposes of illustration and description, it is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications, variations, alterations, substitutions, or equivalent arrangement not hereto described will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. Additionally, while various embodiment of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.