CN216816539U

CN216816539U - In situ oxygen analyzer with solid electrolyte oxygen sensor and auxiliary output

Info

Publication number: CN216816539U
Application number: CN202123214533.4U
Authority: CN
Inventors: 帕夫尔·舒克; 查德·M·麦圭尔; 马修·泰森; 菲利普·奥斯特比
Original assignee: Rosemount Inc
Current assignee: Rosemount Inc
Priority date: 2020-12-21
Filing date: 2021-12-20
Publication date: 2022-06-24
Anticipated expiration: 2031-12-20
Also published as: JP7590583B2; EP4264249A4; EP4264249A1; WO2022140013A1; CN114646676A; JP2024500844A

Abstract

An improved oxygen analyzer, comprising: a controller configured to receive the oxygen sensor signal and provide an oxygen concentration output. A probe configured to extend into a source of combusted process gas. An oxygen sensor disposed within the probe and having a sensing electrode mounted to one side of the solid electrolyte and a reference electrode mounted to an opposite side of the solid electrolyte. The oxygen sensor has a catalytic bead configured to be disposed between the process gas and the sensing electrode. A measurement circuit operably coupled to the oxygen sensor and the controller and configured to provide an oxygen sensor signal to the controller based on an electrical response of the oxygen sensor. The controller is configured to detect behavior of the concentration output of the oxygen sensor over time to provide at least one auxiliary output.

Description

In situ oxygen analyzer with solid electrolyte oxygen sensor and auxiliary output

Technical Field

The present application relates to the field of sensors, and in particular to an in situ oxygen analyzer having a solid electrolyte oxygen sensor and an auxiliary output.

Background

Industrial processes typically rely on energy sources, such as combustion, to generate steam or heat from the feed liquid. Some combustion processes involve the operation of a furnace or boiler. While combustion provides a relatively low cost source of energy, it is often sought in the process to maximize combustion efficiency, as the resulting flue gases exiting the system may be subject to regulatory constraints relating to the emission of harmful gases. Accordingly, one goal of the combustion process management industry is to maximize the combustion efficiency of existing furnaces and boilers, which essentially reduces the production of greenhouse gases and other harmful byproducts.

Electrochemical oxygen sensors based on zirconia are widely used in industrial applications for oxygen measurement. The electrochemical oxygen sensor operates at high temperatures (e.g., 650 ℃ -800 ℃) and measures the excess of oxygen remaining after combustion. The response of the sensor to oxygen concentration differences can be calculated using the Nernst equation with a fixed partial pressure (e.g., using air) on the reference electrode:

where C is a constant related to reference/process side temperature variation and hot junction (junction) in the oxygen probe, R is a universal gas constant, T is the process temperature in degrees kelvin, and F is a faraday constant.

SUMMERY OF THE UTILITY MODEL

An improved oxygen analyzer, comprising: a controller configured to receive the oxygen sensor signal and provide an oxygen concentration output. A probe configured to extend into a source of combusted process gas. An oxygen sensor disposed within the probe and having a sensing electrode mounted to one side of the solid electrolyte and a reference electrode mounted to an opposite side of the solid electrolyte. The oxygen sensor has: a catalytic bead configured to be disposed between a process gas and a sensing electrode. A measurement circuit operably coupled to the oxygen sensor and the controller and configured to provide an oxygen sensor signal to the controller based on an electrical response of the oxygen sensor. The controller is configured to detect behavior of the concentration output of the oxygen sensor over time to provide at least one auxiliary output.

Drawings

FIG. 1 is a schematic diagram of an in situ oxygen analyzer/transmitter with which embodiments of the present invention are particularly useful.

FIG. 2 is a schematic perspective view of a combustion oxygen transmitter to which embodiments of the present invention are particularly applicable.

Fig. 3 is a graph indicating a gas concentration percentage versus an oxygen concentration percentage to show an effect of performing combustion control using only oxygen and an effect of performing combustion control using both oxygen and carbon monoxide.

Fig. 4 is a graph showing oxygen analyzer response for different oxygen concentrations in the range of 2% to 10%.

FIG. 5 is a schematic cross-sectional side view of a zirconia-based oxygen sensor according to an embodiment of the present invention.

Fig. 6 is a graph showing the oxygen analyzer step response for different levels (ranging from 0% to 1.0%) of carbon monoxide at 5% oxygen.

Fig. 7 is a graph showing changes in oxygen analyzer readings in the presence of 1% carbon monoxide.

Fig. 8 is a graph of oxygen analyzer reading change linearly with carbon monoxide concentration.

Fig. 9 is a graph showing oxygen analyzer response in the range of 0% to 1% carbon monoxide using an old or obsolete oxygen sensor in a 5% oxygen environment.

Fig. 10 is a graph showing oxygen analyzer response to 1% carbon monoxide.

Fig. 11 is a graph showing oxygen analyzer response to methane.

FIG. 12 is a graph showing the presence of 0.1% -1.5% CH₄Temporal oxygen analyzer reading changeAnd (5) changing the graph.

Fig. 13 is a graph showing a decline line in oxygen analyzer readings as a function of methane concentration.

Fig. 14 is a graph showing a methane concentration dependent oxygen analyzer reading droop line for an old or obsolete oxygen sensor cell.

Fig. 15 is a graph illustrating oxygen analyzer cross-sensitivity (cross-sensitivity) for carbon monoxide in the process.

FIG. 16 is a block diagram illustrating a method of providing combustion control using an advanced in situ oxygen analyzer according to an embodiment of the utility model.

FIG. 17 is a system block diagram of the electronics of the improved oxygen analyzer, according to an embodiment of the present invention.

FIG. 18 is a flow chart of a method of operating a zirconia based oxygen combustion analyzer in accordance with an embodiment of the present invention.

Detailed Description

FIG. 1 is a schematic diagram of an in situ oxygen analyzer/transmitter with which embodiments of the present invention are particularly useful. Transmitter 10 can be, for example, a Model 6888 oxygen transmitter available from Rosemount Inc. (Emerson Automation Solutions Company). Transmitter 10 includes a probe assembly 12 disposed substantially within a stack or chimney 14 of a combustion process. Transmitter 10 is configured to measure the concentration of oxygen within flue gas resulting from combustion occurring at combustor 16. The combustor 16 may be operatively coupled to an air or other oxygen source 18, and a combustion fuel source 20. The combustion controller 22 is operatively coupled to the oxygen valve 24 and the fuel valve 20. Based on signals from combustion controller 22, valve 18 and/or valve 20 control the air and/or fuel supplied to the combustion process occurring at combustor 16. Combustion controller 22 receives an indication of oxygen in the flue gas from transmitter 10 and uses the indication to provide efficient and environmentally friendly control of the combustion process. Because transmitter 10 is configured to be exposed to a combustion zone, transmitter 10 can be configured to withstand high temperatures.

FIG. 2 is a schematic perspective view of a combustion oxygen transmitter to which embodiments of the present invention are particularly applicable. Transmitter 100 includes a housing 102, a probe 104, and electronics 106. Transmitter 100 is typically coupled to a stack or flue gas wall using flange 120.

The probe 104 includes a distal end 108 to which is mounted a diffuser or filter 110. The diffuser 110 is a physical device configured to allow at least some gas to diffuse through, but otherwise protect the components within the probe 104. Specifically, diffuser 110 protects a solid electrolyte based oxygen measurement cell or sensor 112. The oxygen measurement cell 112 uses a solid electrolyte such as zirconia or bulk ceramic that provides a measured potential or measured current indicative of the oxygen partial pressure relative to a reference oxygen partial pressure when the cell 112 is operating within its thermal operating range. The electronics 106 are generally configured to provide thermal control to the probe 104 using electric heaters and temperature sensors (not shown). Further, the electronics 106 are configured to obtain a measured current or measured potential response of the cell 112 and calculate the oxygen output. In one example, the electronics 106 use a known Nernst equation (set forth above) for such calculations.

An in situ oxygen analyzer such as transmitter 100 having a measured potential zirconia sensor 112 is very robust and can operate in a combustion environment for years. Under ideal combustion conditions, oxygen and fuel are combined in an ideal ratio to produce primarily carbon dioxide (CO)₂) And water (H)₂O) and trace amounts of other gases from fuel impurities and nitrogen oxides, e.g. sulfur dioxide (SO)₂) And Nitrogen Oxides (NO)_x). This stoichiometric point with the highest efficiency and lowest emissions is very difficult to achieve in actual combustion due to imperfect fuel/air homogeneity and fuel energy density and fuel/air flow variations. Typical flue gas oxygen excess concentrations are approximately 2-3% for gas burners and approximately between 2-6% for boilers and oil burners. The optimum operating point is considered to be somewhere between 1% and 6% excess oxygen concentration. This optimum operating point depends on the boiler load and the firing rate, which is influenced by the fuel velocity. Unfortunately, unburned fuel and carbon monoxide are produced at 1000+ PPM (part per million) levelsAre not detectable by current oxygen analyzer technology and can potentially create safety issues and difficulties for combustion control at lower oxygen concentration settings.

Function generator curves are typically developed from test data to specify the ideal oxygen trim control point based on firing rate index, fuel or steam flow. It is generally believed that the most efficient and safe combustion occurs in the range of 0.75% to 2% oxygen excess without dangerous local reduction situations, which are difficult to control using oxygen alone in combustion. Furthermore, any leakage in the walls of the boiler or combustion appliance would allow additional oxygen penetration, thereby undermining oxygen concentration and combustion control. While effective combustion control may be achieved with oxygen measurements alone, combustion efficiency and stability may be improved with concurrent measurements of carbon monoxide (CO). Operation at trace CO levels near about 100PPM to 200PPM and small amounts of excess air will indicate that the combustion conditions are near the stoichiometric point with the highest efficiency.

Carbon monoxide sensors and sensing equipment are commercially available for applications ranging from worksite safety to exhaust gas analysis. Unfortunately, none of them provide a reliable in situ carbon monoxide measurement for the combustion process. In addition, chemical gas sensors have been studied on the basis of semiconductor oxides for combustible gas detection. This type of sensor is known as a Taguchi sensor and uses solid state devices made of sintered n-type metal (iron, zinc and tin) oxides, but has poor selectivity for use in combustion systems and insufficient long term stability. Furthermore, Infrared (IR) absorption techniques that rely on the measurement of infrared light absorption may be used, but would require relatively complex and expensive flue gas conditioning systems. Another type of sensor that can potentially provide carbon monoxide information is known as a tunable diode laser spectroscopy sensor, where the laser light passes through the sensor. However, such sensors would require a relatively powerful laser, and such sensors would still suffer from aberrations in heavy particle loading, broad background radiation from the fireball, and require temperature and pressure compensation, and are very costly. The solid-state electrochemical mixed potential zirconia technology invented in the 1970 s has been shown to be not very reliable in challenging and severe combustion environments. The only in situ carbon monoxide probes available on the market are currently based on mixed potential zirconia technology and developed for very clean gas combustion applications.

According to embodiments described herein, a combustion oxygen analyzer is provided with the ability to monitor signals from a zirconia-based oxygen sensor over time to provide additional output related to one or more non-oxygen gases. Examples of such non-oxygen gases include carbon monoxide and combustibles. The embodiments described herein generally have a normal operating mode in which the oxygen analyzer obtains a signal from a zirconia-based oxygen sensor and provides an indication of the remaining oxygen in the combustion process very accurately using a sensor output that is logarithmically dependent on the oxygen concentration according to the nernst equation set forth above.

Fig. 4 is a graph showing oxygen analyzer response for different oxygen concentrations in the range of 2% to 10%. A limitation of oxygen measurement using zirconia technology is that the correct oxygen level cannot be measured in the presence of high concentrations of combustible gases. When present, these gases indicate irregular and dangerous combustion. Zirconia sensors read lower in the presence of combustibles due to oxygen consumption in the combustion reaction at the process electrode. Fig. 4 shows the normal operating mode of the oxygen analyzer and provides a very accurate signal indicative of the oxygen concentration as the oxygen varies from 2% (bottom left) to 10% (top right).

According to an embodiment of the utility model, the oxygen analyzer has a second mode in which the behavior of the oxygen sensor over time is analyzed to detect and/or quantify one or more non-oxygen gases in the flue.

FIG. 5 is a schematic representation of an embodiment in accordance with the utility modelA schematic cross-sectional side view of an exemplary zirconia-based oxygen sensor. As shown in FIG. 5, the oxygen sensor 212 includes a process gas inlet 213, the process gas inlet 213 being open or exposed to a gas having an oxygen concentration p (O)₂) Is provided (schematically shown at reference numeral 214) that diffuses or otherwise passes through the catalytic beads 216 to enter the cermet sensing electrode 218, the cermet sensing electrode 218 preferably being formed at least in part from platinum. The zirconium oxide layer 220 allows oxygen ions to move from the cermet sensing electrode 218 to the reference electrode 222, the reference electrode 222 being configured to have an oxygen concentration p (O)₂) ' reference gas (e.g. air (20.9% O)₂) ) contact. The reference electrode 222 is also preferably formed at least in part from platinum. This oxygen sensor 212 is configured to be disposed in the distal end 108 of the in situ oxygen sensing probe 104, so the process gas 214 is or includes flue gas from combustion. The catalytic beads 216 are used to protect the cermet sensing electrode 218 in a reducing atmosphere and a high sulfur environment. The catalytic beads may be formed at least in part from platinum deposited or otherwise secured to a ceramic substrate. When the zirconia 220 is at its operating temperature, on the process gas side p (O)₂) And reference gas side p (O)₂) The difference in oxygen partial pressure between' will produce a measured potential response between the cermet electrode 218 and the cermet electrode 220.

During regular, well-controlled combustion, the combustible concentration is very low (not more than 200 ppm) or 0.02%. In this case, the oxygen regulation is relatively smooth without any sharp abnormal oxygen concentration drop (less than 0.2%/min). When irregular control or combustion instabilities occur, particularly when the carbon-based fuel is mixed with an insufficient amount of oxygen to complete the reaction, the process will result in the formation of carbon monoxide, thus indicating incomplete combustion:

an oxygen sensor with a catalytic electrode membrane and beads will convert carbon monoxide and residual fuel formed during combustion, thus consuming oxygen reaching the sensing electrode 218 according to the following chemical formula:

unlike regular combustion, which fine-tunes the oxygen concentration very smoothly down to the control point, these two reactions will drastically reduce (within approximately 5 seconds) the analyzer's oxygen concentration reading. According to these reactions, the ideal oxygen concentration will drop by half the carbon monoxide concentration or approximately twice the methane concentration, resulting in four times the oxygen consumption associated with methane.

This oxygen concentration reduction in the cermet electrode and catalytic beads during the combustion reaction is used for accurate and reliable carbon monoxide and unburned fuel (CH) according to embodiments of the present invention₄) And (6) detecting. The embodiments described herein will facilitate more efficient setting of oxygen concentration control and safe fine tuning of oxygen concentration in combustion. Sharp O of the analyzer with the appearance of carbon monoxide as a first product of incomplete combustion₂The drop in reading is a leading indication of the presence of carbon monoxide within milliseconds of breakthrough of combustion.

Fig. 6 is a graph showing the oxygen analyzer step response for different levels (in the range of 0% to 1.0%) of carbon monoxide at 5% oxygen. Fig. 7 is a graph showing the change in oxygen analyzer readings in the presence of 1% carbon monoxide. As can be seen from fig. 6 and 7, the oxygen sensor response to carbon monoxide is highly reproducible, up to 1% carbon monoxide, linearly dependent on carbon monoxide concentration.

Fig. 8 is a graph of oxygen analyzer reading change linearly with carbon monoxide concentration. As shown in fig. 8, the CO concentration can be calculated as a function of the change in the oxygen concentration value when the CO concentration is in the range of 0.0% -1.0%. In the example shown in fig. 8, the CO concentration is equal to-2.17 times the change in oxygen concentration.

Fig. 9 is a graph showing oxygen analyzer response in the range of 0% to 1% carbon monoxide using an old or obsolete oxygen sensor in a 5% oxygen environment. With an oxygen analyzer according to embodiments described herein, carbon monoxide is reproducibly detected even with old or worn oxygen sensors (i.e., sensors that fail oxygen calibration and do not have a very reliable oxygen measurement). This is due at least in part to the catalytic beads 216 in the oxygen sensor.

Fig. 10 is a graph showing oxygen analyzer response to 1% carbon monoxide. As can be seen, the oxygen analyzer response to carbon monoxide is very fast (on the order of approximately 10 seconds for 90% response). This response to carbon monoxide is considered reliable considering that the oxygen trim is very smooth and the result of the oxygen rate of change is 10 times this value. Higher oxygen concentrations or lower carbon monoxide or methane concentrations for more efficient CO/CH₄The contribution of combustion will be small but the conversion will exceed 90% even at low (roughly 1.5%) oxygen concentrations.

Fig. 11 is a graph showing oxygen analyzer response to methane. Similar to carbon monoxide detection, an oxygen analyzer according to embodiments described herein may detect unburned fuel, such as methane (CH), based on a sharp (approximately 10 seconds) drop in oxygen readings₄). The methane and carbon monoxide conversion on the oxygen sensor cermet sensing electrode 218 and catalytic bead 216 is close to 100%, with very rapid (0.1% -0.4% O relative to carbon monoxide)₂Drop-see fig. 10) greater than 1% oxygen drop associated with methane, as shown in fig. 11.

FIG. 12 is a graph showing the presence of 0.1% -1.5% CH₄Graph of oxygen analyzer reading change in time. Fig. 13 is a graph showing a decline line in oxygen analyzer readings as a function of methane concentration. As shown in fig. 13, the methane concentration can be calculated as a function of the change in the oxygen concentration value when the methane concentration is in the range of 0.0% -1.5%. In the example shown in fig. 13, the methane concentration is equal to-0.486 times the change in oxygen concentration.

Fig. 14 is a graph showing a methane concentration dependent oxygen analyzer reading droop line for an old or obsolete oxygen sensor cell. The oxygen analyzer sensitivity to methane is very good and depends linearly on methane concentration (as shown in fig. 12-14), and allows uncalibrated methane detection even with aged oxygen sensors. Further, as shown in fig. 14, the relationship between the change in oxygen concentration and the methane concentration may be affected by the change in oxygen concentration (fig. 14 shows a comparison of 2% and 5%). Therefore, when providing the methane concentration as a function of a change in the oxygen concentration, it is useful to adjust the relationship based on the most recently measured oxygen concentration. In the example shown in fig. 14, when the oxygen concentration is at 5%, the methane concentration is-0.506 times the change in the oxygen concentration. However, when the oxygen concentration is 2%, the methane concentration is-0.585 times the change in the oxygen concentration.

Given the much greater oxygen consumption in the combustion reaction with methane, an oxygen analyzer according to embodiments described herein will provide a reliable indication of carbon monoxide breakthrough with oxygen levels falling as high as 0.5%, and unburned fuel detection with oxygen concentrations falling greater than 0.5%. This new advanced oxygen analyzer feature will provide an effective oxygen trim option for efficient, reliable and safe combustion control.

FIG. 15 is a graph illustrating oxygen concentration percentage, carbon monoxide concentration, and oxygen/carbon monoxide optimization during combustion. This allows for efficient diagnosis of combustion process problems (e.g., faulty burners, induced draft fans, and/or fuel/air mixture imbalances). Because the oxygen analyzer according to embodiments described herein monitors oxygen concentration, the rate of change of the oxygen concentration readings is monitored by electronics and/or software. If the measured drop in oxygen concentration is in the range of 0.2% -0.4% over a time span of approximately 5-10 seconds, this would indicate the presence of carbon monoxide, and a carbon monoxide algorithm may be applied to the oxygen sensor readings to calculate the carbon monoxide concentration based on the drop. Additionally or alternatively, an alarm may be set, which may be configured to indicate "carbon monoxide high". If the oxygen concentration readings are changed in the same time spanThe magnitude of the variation is greater than 0.5%, the oxygen analyzer will indicate the presence of methane or equivalent combustibles in the flue gas, and different calculations will be used to calculate the methane concentration and/or set the "CH"₄High alert ".

FIG. 16 is a schematic diagram of in situ oxygen analyzer operation according to an embodiment of the utility model. At block 400, the analyzer measures an online oxygen measurement, initially trimming the oxygen concentration down to less than 10%. Subsequently, during normal oxygen measurement operations, the oxygen analyzer detects a relatively sharp drop in the oxygen sensor reading over a 5 second time period. As shown in fig. 16, if the drop in reading is between 0.2% and 0.4% oxygen concentration, control proceeds along line 402 to block 404 where an indication is provided that carbon monoxide is breaking through the process. Further, at block 404, the analyzer may apply a carbon monoxide detection algorithm and calculate a specific carbon monoxide concentration based on the signal from the zirconia-based oxygen sensor. The controller may send an alert to a control room controlling the combustion process via any suitable wired or wireless communication so that remedial action may be taken. In one example, as shown at block 406, the control room may responsively add oxygen to the combustion system to address the carbon monoxide breakthrough.

Further, as shown in FIG. 16, if the oxygen sensor reading drops by more than 0.5% oxygen concentration over a 5 second period, control proceeds along line 408 to block 410 where an indication of unburned fuel detection is provided at block 410. Further, at block 410, the analyzer may apply a methane (or combustible) detection algorithm to actually calculate the methane concentration. Further, an alarm may be sent to the control room indicating the presence and/or concentration of methane or combustibles in the flue gas. Remedial action may then be taken as indicated at block 412, where the burner of the combustion appliance may be checked, the flow of fuel may be stopped, and the system may be re-ignited under safe conditions.

FIG. 17 is a system block diagram of electronics 106 within an improved oxygen analyzer, according to an embodiment of the present invention. The electronic device 106 includes a controller 500, and in some embodiments, the controller 500 may be a microprocessor. The controller 500 is coupled to measurement circuitry 502, and the measurement circuitry 502 may include suitable amplification, linearization (linearization), and analog-to-digital conversion circuitry to obtain a measured potential response from an oxygen sensor 504 coupled to the measurement circuitry 502. Measurement circuitry 502 provides controller 500 with a digital indication of the measured potential response of oxygen sensor 504. The controller 500 can calculate the oxygen concentration output using the well-known Nernst equation set forth above. Further, the controller 500 can evaluate the time-based response of the measured potential signal of the oxygen sensor 504 to provide a carbon monoxide breakthrough and/or combustible indication as described above. In one embodiment, the controller 500 may store or otherwise detect a difference in the measured potential response of the oxygen sensor 504 over a defined period of time (e.g., 5 seconds or 10 seconds). This difference in response over a defined period of time may then be compared to one or more selected thresholds to provide the above-described assistance (i.e., non-oxygen related) output.

In one example, the controller 500 may be a microprocessor programmed to execute a sequence of instructions that simply obtains a measured potential response at a first time and a second measured potential response at a preselected duration (e.g., 5 seconds) later than the first time. The two measured potential responses may then be compared to determine if the difference exceeds one or more of the selected thresholds. Of course, other techniques for evaluating the time-based response of the potential signal of the oxygen sensor may be used.

Controller 500 is also coupled to communication circuitry 506 to provide the oxygen analyzer with the ability to communicate over the appropriate process communication segment or loop. The process communication may be via a wired connection or a wireless connection. Process communications are a type of communications particularly suited for real-time process control. Examples of process communications include, but are not limited to, communications in accordance with the Highway Addressable Remote transmitter

Protocol or FOUNDATION^TMCommunication of the Fieldbus bus protocol. However, according to embodiments of the present invention, it is possible to useOther suitable process communication protocols, wired and/or wireless. Further, embodiments described herein may also include transmitting information according to a wireless process communication protocol (e.g., IEC 62591).

Further, the controller 500 is coupled to a user interface 508, and the user interface 508 may be provided in the form of: an oxygen concentration reading on the exterior of the housing of the transmitter, and any suitable operator input devices (e.g., buttons, knobs, dials, etc.). Further, in some embodiments, the electronics 106 may include a heater control circuit 510, the heater control circuit 510 coupled to the controller 500 to provide energy to a heater within the probe to maintain the oxygen sensor within an effective thermal operating range, such as 650-800 degrees celsius.

FIG. 18 is a flow chart of a method of operation of a zirconia based oxygen combustion analyzer in accordance with an embodiment of the present invention. The method 600 begins at block 602, where a combustion analyzer measures oxygen sensor values over a defined period of time (e.g., 5 seconds). Next, at block 604, the combustion analyzer calculates a difference in oxygen sensor values over a defined period of time. Next, at block 606, the calculated difference is compared to a first threshold, such as to determine whether the difference is greater than 0.5% oxygen concentration. If this occurs, control proceeds along line 608 to block 610, at block 610, the combustion analyzer begins generating a combustible or unburned fuel (methane) warning, and causes controller 500 to calculate a concentration of combustible (e.g., methane) in the process gas using a combustible algorithm based on the oxygen sensor measured potential response. As described above, this would allow the person responsible for combustion control to check the burner, stop fuel flow, and re-ignite under safe conditions.

As shown in fig. 18, the method 600 further includes comparing the calculated difference to a second threshold or band (band), as shown at block 612. For example, the second threshold or band may be an oxygen concentration value difference in the range of 0.2% to 0.4%. If the difference is within the band, control proceeds along line 614 to block 616 where a second warning, such as a carbon monoxide breakthrough warning, is provided at block 616. Further, the controller 500 may switch to begin using a different calculation than the Nernst equation, which uses the measured potential response of the oxygen sensor to provide an indication of carbon monoxide concentration.

As described above, a zirconia-based oxygen analyzer design is provided that is capable of providing reliable oxygen concentration measurements, as well as advanced unburned fuel detection and carbon monoxide detection in combustion flue gases. The zirconia oxygen sensors used in these examples typically employ a catalytically active cermet electrode and protective catalytic beads against combustible materials (e.g., CH) in the zirconia oxygen sensor package₄) And CO, to drastically reduce the oxygen concentration in the cell in approximately 5-10 seconds. The sharp drop in the signal of the oxygen analyzer is analyzed and developed by a rate of change algorithm based on an oxygen smoothing trim as part of the combustion control to provide a reliable indication of no calibration of the detection of unburned fuel (e.g., methane) and carbon monoxide in the process. The embodiments described herein generally provide effective oxygen trim options for efficient, reliable, and safe combustion control, thus facilitating diagnostics of process issues (e.g., malfunctioning combustors, fuel/air mixture imbalances, and induced draft fans).

Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the utility model.

Claims

1. An oxygen analyzer, comprising:

a controller configured to receive an oxygen sensor signal and provide an oxygen concentration output;

a probe configured to extend into a source of combusted process gas;

an oxygen sensor disposed within the probe, the oxygen sensor having a sensing electrode mounted to one side of a solid electrolyte and a reference electrode mounted to an opposite side of the solid electrolyte, the oxygen sensor further having a catalytic bead configured to be disposed between the process gas and the sensing electrode;

a measurement circuit operatively coupled to the oxygen sensor and the controller, the measurement circuit configured to provide the oxygen sensor signal to the controller based on an electrical response of the oxygen sensor; and is

Wherein the controller is configured to detect behavior of the concentration output of the oxygen sensor over time to provide at least one auxiliary output.

2. The oxygen analyzer of claim 1, wherein the sensing electrode is a cermet sensing electrode.

3. The oxygen analyzer of claim 2, wherein the measurement circuit is configured to measure a voltage between the cermet sensing electrode and a cermet reference electrode.

4. The oxygen analyzer of claim 2, wherein the cermet sensing electrode and the catalytic bead are formed at least in part from platinum.

5. The oxygen analyzer of claim 1, wherein the solid electrolyte is a zirconia layer.

6. The oxygen analyzer of claim 1, wherein the solid-state electrolyte is a bulk ceramic.

7. The oxygen analyzer of claim 1, wherein the at least one auxiliary output is an alarm indicative of unburned fuel.

8. The oxygen analyzer of claim 1, wherein the at least one auxiliary output is an alarm indicative of carbon monoxide.

9. The oxygen analyzer of claim 1, wherein the auxiliary output is transmitted to a remote device to trigger a change in fuel to oxygen ratio associated with combustion.

10. The oxygen analyzer of claim 7, further comprising: a process communication module operatively coupled to the controller, the process communication module configured to transmit the auxiliary output using process communication.

11. The oxygen analyzer of claim 1, wherein the controller is further configured to: calculating a concentration of a non-oxygen gas in the process gas based on behavior of a concentration output of the oxygen sensor over time.