JPH0249657B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for measuring oxygen partial pressure or concentration, and in particular to a method and apparatus for measuring oxygen partial pressure or concentration, in particular, using a plurality of oxygen sensors each having electrodes on both sides of a solid electrolyte having oxygen ion conductivity. The present invention relates to a method and an apparatus for measuring oxygen partial pressure or concentration at different locations in the measurement depth direction from the flow of a gas to be measured.

Conventionally, the principle of oxygen concentration batteries that utilize electrochemical reactions using solid electrolytes such as zirconia that conduct oxygen ions at high temperatures has been used to reduce the amount of gas discharged from various steelmaking furnaces, other industrial furnaces, boilers, etc. It is known to detect the oxygen concentration (oxygen partial pressure) in the combustion exhaust gas and control the combustion status of those furnaces and boilers.

By the way, in this type of oxygen sensor, porous platinum electrodes are provided on both sides of a zirconia solid electrolyte of a predetermined shape, and the electrode on one side is brought into contact with the atmosphere as a standard comparison gas to obtain a reference oxygen concentration ( The oxygen concentration (partial pressure) between the reference electrode and the measurement electrode is used as the reference electrode, while the other side electrode is exposed to the combustion exhaust gas, which is the gas to be measured, and is used as the measurement electrode. By measuring the electromotive force based on the difference, the oxygen concentration (partial pressure) in the gas to be measured is measured. Furthermore, the electromotive force generated between such two electrodes:
E is expressed by the following equation (1), which is called the Nernst equation.

E=-RT/nF×2.303×logPo ₂ (S)/Po ₂ (A) ……(1) However, R: Gas constant T: Absolute temperature n: Number of electrons F: Faraday constant Po ₂ (S): Measurement Oxygen partial pressure in target gas Po ₂ (A): Oxygen partial pressure in standard comparison gas.

Then, among the equation (1), R, T, n, F,
Since Po ₂ (A) can be treated as a constant,
By measuring the electromotive force: E, the oxygen partial pressure: Po ₂ (S) in the gas to be measured can be determined.

In addition, regarding the oxygen concentration, equation (1) is as follows:
It is possible to rewrite equation (2) as shown below.

E=-0.0469×T× _logO2 (%, S)×P(S)/ _O2 (%, A)×P(
A)...(2) However, O ₂ (%, S): Oxygen concentration in the measurement target gas P (S): Pressure of the measurement target gas O ₂ (%, A): Oxygen concentration in the standard comparison gas P (A): Pressure of standard comparison gas.

By the way, the gas to be measured, such as furnace combustion exhaust gas, which is the measurement target of conventional oxygen sensors that utilize such electrochemical reactions, flows in a layered manner in passages such as flues, so it is difficult to measure. It is recognized that the value of oxygen concentration varies greatly depending on the depth of the point. For this reason, conventionally, the oxygen concentration has been measured at one point in the approximate center of the flue. However, given that most of the combustion exhaust gas passes through the central part because the flow velocity is high in the central part, it was thought that the representative value of the oxygen concentration of the combustion exhaust gas was being measured. However, with such conventional methods, although trends in changes in oxygen concentration in combustion exhaust gas can be grasped, it is difficult to accurately determine oxygen concentration.

Incidentally, the pressure of combustion exhaust gas: P(S) differs depending on, for example, whether the furnace is operated under high load or low load, and also differs depending on the type of furnace. Therefore, if the air pressure: P(A) is constant, P(S) changes in the above equation (2), so the value of the electromotive force: E changes, Therefore, even if O ₂ (%, S) does not change, the oxygen concentration: O ₂ (%, S) determined from the value of E according to Nernst's equation will change.

The present invention has been made against this background, and its purpose is to calculate the oxygen partial pressure from the flow of the gas to be measured.
Another object of the present invention is to provide a method and apparatus that can more accurately measure oxygen concentration.

In order to achieve this object, the present invention has a measurement electrode that is brought into contact with the gas to be measured on one side of the solid electrolyte that has oxygen ion conductivity, and a reference oxygen source on the other side. A plurality of oxygen sensors each having a reference electrode that is brought into contact with a standard comparison gas having a partial pressure or concentration are arranged at a predetermined distance in the depth direction with respect to the flow of the gas to be measured; to the reference electrode portion of each oxygen sensor through a supply tube of the standard comparison gas which is continuously discharged into the flow of the gas to be measured and maintained at a pressure substantially equal to the pressure of the gas to be measured. Oxygen partial pressure or concentration at different locations in the measurement depth direction is measured by each of the oxygen sensors.

Therefore, according to the method of the present invention, the oxygen partial pressure or concentration of the gas to be measured at different locations in the measurement depth direction can be effectively determined, and based on these measured values, This makes it possible to obtain more accurate values of the oxygen partial pressure or concentration than when measuring a representative value at one point in the flow of the gas to be measured.

In addition, in the present invention, in order to implement such a method, (a) a reference oxygen partial pressure that is inserted and installed in the depth direction of the flow of the gas to be measured, and that is continuously introduced; Or a pipe configured to continuously discharge a standard comparison gas of concentration into the flow of the gas to be measured from the discharge port so that the pressure of the standard comparison gas in the pipe is approximately equal to the pressure of the gas to be measured. (b) a solid electrolyte with oxygen ion conductivity, a measuring electrode provided on one side thereof, and a reference electrode provided on the other side, the measuring electrode flowing outside the main pipe. The reference electrode is attached to the wall of the main pipe at a predetermined distance in the pipe axis direction so that it is brought into contact with the gas to be measured, and the reference electrode is brought into contact with a standard comparison gas flowing through the main pipe. A device that includes a plurality of oxygen sensors and that measures oxygen partial pressure or concentration at different locations in the measurement depth direction using the plurality of oxygen sensors is preferably used.

Hereinafter, in order to clarify the present invention more specifically, its configuration will be explained in detail with reference to the drawings.

First, in FIG. 1, 1 is a main pipe, and a plurality of oxygen sensors are attached to the main pipe 1 at predetermined intervals inside an oxygen sensor cover 2 for preventing damage to the oxygen sensors. In addition, in order to attach this oxygen sensor to the main pipe 1, a sensor back cover 3 is provided on the main pipe 1 portion corresponding to the oxygen sensor cover 2, and the oxygen sensor can be attached to the main pipe by removing the sensor back cover 3. It is designed so that it can be attached and detached freely. Note that these oxygen sensors are arranged at a predetermined distance from the main pipe 1 in the pipe axis direction, and the arrangement interval is generally 50 cm or more.
In the example device, they are spaced 1 m apart. The main pipe 1 is made of an integral pipe material having such a length that the oxygen sensor provided at its tip reaches approximately the center of the flow of the gas to be measured.

In addition, air as a standard comparison gas is continuously introduced into the main pipe 1 in a small amount through a relatively high pressure air passage through a throttle valve (not shown). Furthermore, the air introduced in this way into the main pipe 1
Air is continuously released from an air release port 4 provided at the tip of the air. Furthermore, a mounting flange 5 and a terminal box 8 are attached to the base of the main pipe 1.

The main pipe 1 is then inserted and installed into the flow of combustion exhaust gas, which is the gas to be measured, at a measurement point such as a flue of a boiler. That is, as shown in the figure, the main pipe 1 is attached to a furnace wall flange 6 provided on a furnace wall 7 by a mounting flange 5. Note that the terminal box 8 is provided with wiring and piping holes 9, and although the wiring and piping are not shown in FIG. 1, they are properly performed.

Further, FIG. 2 shows how the oxygen sensor is attached to the main pipe 1, and FIG. 3 shows the following:
An example of the structure of such an oxygen sensor is shown enlarged. In these figures, a zirconia sensor 11 as an oxygen sensor is fixed to a sensor fastener 13 at its base, and its cylindrical body is mounted at a predetermined mounting position provided in the main pipe 1, as shown in FIG. The inside is opened so as to communicate with the inside of the main pipe 1, and the sensor holding fitting 14 is used to airtightly mount the sensor. The zirconia sensor 11 is attached and detached by removing the sensor back cover 3 provided on the main pipe 1, as described above. Furthermore, a filter 10 is attached to the outside of the zirconia sensor 11 to prevent dust from passing through.
The oxygen sensor cover 2 provided on the outside of the filter 10 and the zirconia sensor 11 can be prevented from being damaged. Furthermore, a zirconia sensor 11 as an oxygen sensor
A calibration gas pipe 12 is provided for testing the electromotive force of the zirconia sensor 11, and the calibration gas supplied through the calibration gas pipe 12 is supplied to the side of the zirconia sensor 11 that is brought into contact with the gas to be measured.
This allows the electromotive force of such a sensor to be tested.

Further, an oxygen sensor such as the zirconia sensor 11 has a measurement electrode on one side and a reference electrode on the other side of a solid electrolyte that has oxygen ion conductivity at high temperatures. Note that any of the solid electrolytes used in conventional oxygen sensors that utilize electrochemical reactions can be used as this solid electrolyte, such as solid electrolytes with calcium oxide dissolved in zirconium oxide, Examples include those in which yttrium oxide is dissolved in zirconium, those in which yttrium oxide is dissolved in thorium oxide, and those in which lanthanum oxide is dissolved in cerium oxide. In addition, the shape of the solid electrolyte can be a cylinder with a bottom (test tube shape) as shown in FIG. It will be done.

Then, one side of the solid electrolyte having a predetermined shape is brought into contact with the gas to be measured such as combustion exhaust gas, while the other side is exposed to the reference oxygen partial pressure or concentration. The standard comparison gas, usually the atmosphere (air), is brought into contact with it, but if the solid electrolyte is cylindrical or has a cylindrical shape with a bottom, the gas to be measured is generally brought into contact with the outer surface of the solid electrolyte. The inner surface will be configured to be in contact with the atmosphere.

Furthermore, the measurement electrodes and reference electrodes provided on each side of the solid electrolyte are porous metal electrodes similar to those provided in conventional oxygen sensors, and are generally made of platinum electrodes. is preferably used, but other metal materials such as platinum/rhodium alloy, platinum/palladium alloy, silver, platinum/silver alloy, etc. may be used without any problem. Further, such a porous metal electrode may be coated with a certain ceramic. In the zirconia sensor 11 illustrated in FIG. 3, the outer electrode 16 as the measurement electrode and the inner electrode 18 as the reference electrode are as follows.
Both are made of platinum.

The zirconia sensor 11 is hermetically fixed to the sensor clasp 13, and its outer electrode 16 is electrically connected to the sensor clasp 13 through the outer electrode connecting portion 17. Furthermore, the electrical signal from the inner electrode 18 is guided to a lead wire 20 via the outer electrode connecting portion 19 and taken out by the lead wire 20.

Note that an electric heater 15 is attached to the inside of the zirconia sensor 11 with a support 22.
By supplying power through the electric heater lead wire 21, the electric heater 15 heats the zirconia sensor 11 (more specifically, the solid electrolyte) to a predetermined temperature, generally about 500° C. or higher. ing.

Therefore, in a device with such a configuration, the main pipe 1
The four zirconia sensors 11 installed at predetermined intervals in the longitudinal direction of the sensor are brought into contact with the gas to be measured at different depths within the flow of the gas to be measured. . That is, each zirconia sensor 11 attached to the main pipe 1 inserted and installed in the flow of the gas to be measured is brought into contact with the gas to be measured that has passed through the oxygen sensor cover 2 and the filter 10 at its measurement electrode 16. On the other hand, inside the main pipe 1, air as a standard comparison gas is flowing toward the discharge port 4 at the tip of the main pipe 1, so that the air comes into contact with the inner electrode 18 of the zirconia sensor 11. As a result, electromotive force can be obtained individually from the four zirconia sensors 11 as oxygen sensors. and,
The electromotive force and oxygen partial pressure of this zirconia sensor 11,
Furthermore, the relationship with oxygen concentration can be obtained from the Nernst equation, and from the above equations (1) and (2),
Using the value of this electromotive force, the oxygen partial pressure and eventually the oxygen concentration can be determined.

Incidentally, in this exemplary device, when the four sensors provided in the main pipe 1 are designated S ₁ , S ₂ , S ₃ , and S ₄ from the base on the installation side toward the tip, these S ₁ , S If the measured data of oxygen concentration determined from the electromotive force from ₂ , S ₃ and S ₄ is schematically illustrated, it will be as shown in FIG. In addition, in Fig. 4, the left side shows the oxygen concentration at different measurement depths with respect to the flow of combustion exhaust gas during high-load operation, and the right half shows the oxygen concentration at different measurement depths with respect to the flow of combustion exhaust gas during high-load operation. The oxygen concentration at each location in the exhaust gas is shown. As is clear from FIG. 4, the combustion exhaust gas from the furnace flows in a layered manner in the flue, and the oxygen concentration value varies greatly depending on the depth of the measurement point. The flow velocity of the combustion exhaust gas from the furnace increases in the center of the flue. Therefore, among the values of S ₁ , S ₂ , S ₃ , and S ₄ , by weighting the values in the center of the flue and calculating the average value, in other words, the measured value of each oxygen sensor is By performing a weighted average using a reference, the oxygen concentration in the combustion exhaust gas can be determined more accurately. Note that when the flow velocity in the flue is substantially uniform, the oxygen partial pressure and, by extension, the oxygen concentration can be accurately determined by simply averaging each measured value.

Incidentally, the pressure of the combustion exhaust gas varies depending on the combustion state of the furnace, the type of the furnace, etc. and,
If the pressure of air as the standard comparison gas: P(A) is constant, the pressure of combustion exhaust gas, which is the gas to be measured, P(S) will change in the above equation (2). From this, the value of the electromotive force: E changes, so even if the actual oxygen concentration in the combustion exhaust gas does not change, the oxygen concentration: O ₂ ( %,S)
will begin to fluctuate.

However, in the present invention, air as a standard comparison gas that is made to flow through the main pipe 1 is
The air pressure inside the main pipe 1 is approximately balanced with the pressure of the gas to be measured because the air is continuously released from the air release port 4 at the tip of the main pipe 1, and generally only a small amount is released. be. Note that since a small amount of air is released from the outlet 4 of the main pipe 1, the air pressure is only slightly higher than the pressure of the gas to be measured, but this is ignored as a measurement tolerance. It is possible. In equation (2) above, even if the pressure of the gas to be measured: P(S) changes, the air pressure: P
Since (A) changes in balance with P(S), the electromotive force is:
The value of E does not change, and as a result, the oxygen concentration: O ₂ (%, S) in the gas to be measured can be determined correctly.

Although the method and apparatus of the present invention have been described in detail with respect to one illustrated apparatus, the present invention is by no means to be construed as being limited to such specific example, and it is not intended to deviate from the spirit of the present invention. Unless otherwise specified, the present invention may be subject to various changes, modifications, improvements, etc. based on the knowledge of those skilled in the art, and the present invention includes all such embodiments; It goes without saying.

For example, in the previous example, the main pipe 1 is composed of one integral pipe, but it is also possible to form one main pipe by connecting multiple pipe parts, Furthermore, instead of one main pipe, a plurality of standard comparison gas supply pipes may be used to supply the standard comparison gas to each oxygen sensor.

[Brief explanation of drawings]

FIG. 1 is an external view showing an example of a device according to the present invention, FIG. 2 is a longitudinal sectional view showing the oxygen sensor installation part of the device, and FIG. 3 is an enlarged view showing only the oxygen sensor part. It is a cross-sectional explanatory diagram,
FIG. 4 is a graph schematically showing measured data of oxygen concentration determined from the electromotive force from four oxygen sensors. 1: Main pipe, 2: Oxygen sensor cover, 3: Sensor back cover, 4: Air discharge port, 7: Furnace wall, 10: Filter, 11: Zirconia sensor, 12: Calibration gas pipe, 13: Sensor fastener, 14: Sensor holding metal fitting, 15: Electric heater, 16: Outer electrode, 18:
Inner electrode, 20: lead wire, 22: support body.

Claims (1)

[Scope of Claims] 1. A solid electrolyte with oxygen ion conductivity has a measurement electrode that is brought into contact with a gas to be measured on one side, and a standard comparison gas having a standard oxygen partial pressure or concentration on the other side. A plurality of oxygen sensors each having a reference electrode that can be applied to the oxygen sensor are arranged at a predetermined distance from each other in the depth direction with respect to the flow of the gas to be measured, and the standard comparison gas is connected to the reference electrode portion of each oxygen sensor. The standard comparison gas is continuously discharged into the flow of the gas to be measured and maintained at a pressure substantially equal to the pressure of the gas to be measured, and is continuously supplied through the supply pipe in the measurement depth direction. A method for measuring oxygen partial pressure or concentration, characterized in that the oxygen partial pressure or concentration at different locations is measured by each of the oxygen sensors. 2. The method according to claim 1, wherein the oxygen partial pressure or concentration is determined by weighted averaging of the measured values obtained by measuring with each of the oxygen sensors. 3. The method according to claim 1 or 2, wherein the measurement of oxygen partial pressure or concentration by the oxygen sensor is performed under a state in which the solid electrolyte is heated to 500° C. or higher. 4. The method according to any one of claims 1 to 3, wherein the gas to be measured is a combustion exhaust gas, and the standard comparison gas is air. 5. A standard comparison gas with a standard oxygen partial pressure or concentration that is inserted and installed in the depth direction of the flow of the gas to be measured, while being continuously introduced.
1, which is configured to continuously discharge the gas to be measured from the discharge port into the flow of the gas to be measured so that the pressure of the standard comparison gas in the pipe is approximately equal to the pressure of the gas to be measured;
A measurement object having a main pipe, a solid electrolyte with oxygen ion conductivity, a measurement electrode provided on one side thereof, and a reference electrode provided on the other side, the measurement electrode flowing outside the main pipe. on the wall of the main pipe, such that the reference electrode is brought into contact with a standard comparison gas flowing through the main pipe;
It includes a plurality of oxygen sensors installed at a predetermined distance in the direction of the tube axis, and the oxygen partial pressure or concentration at different locations in the measurement depth direction is measured by the plurality of oxygen sensors. An oxygen partial pressure or concentration measuring device characterized by: 6. The device according to claim 5, wherein the oxygen sensor is detachably attached to the main pipe. 7. The device according to claim 5 or 6, wherein the discharge port is provided at a distal end of the main pipe. 8. Any one of claims 5 to 7, characterized in that the oxygen sensor is equipped with a heating means, and is configured such that the solid electrolyte can be heated to a predetermined temperature by the heating means. The device described in.