JPH0552802A - CO gas continuous measuring device - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a continuous CO gas concentration measuring device which is stable in operation, highly reliable, and capable of continuously and accurately measuring CO gas in a measurement gas. [Composition] An inner electrode made of a non-catalytic electrode for detecting CO gas in a measurement gas, and an outer electrode made of a porous platinum catalyst mounted on the outside of a zirconia tube and supplied with a comparative gas,
Provide a ring-shaped positive contact that contacts the lead wire of the inner electrode and a ring-shaped negative contact that is made of non-catalytic gold wire that contacts the lead wire of the outer electrode. The concentration of CO gas in the measurement gas is determined from the electromotive force generated during the period.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for continuously measuring the concentration of CO gas, and more specifically, CO contained in the measurement gas.
C that enables continuous and accurate measurement of gas concentration
The present invention relates to a continuous measuring device of O gas concentration.

[0002]

2. Description of the Related Art Generally, in the combustion process, from the viewpoint of energy saving and pollution prevention, the concentration of combustible gas (CO etc.) and oxygen contained in the combustion exhaust gas flowing through the flue is constantly monitored to ensure that the combustion furnace is in an optimum state. Combustion is controlled so that it is operated.

Conventionally, the following device has been used to continuously measure the concentration of CO gas contained in the combustion exhaust gas flowing through the flue. That is, an inner electrode and an outer electrode are provided in a zirconia tube composed of a zirconia solid electrolyte composed of an oxygen ion conductor, and an inner electrode into which a measurement gas enters is composed of a non-catalytic electrode and an outer electrode into which a comparison gas enters is catalyzed. The electrode is configured to have a strong function, and the CO gas concentration in the measurement gas is obtained from the electromotive force of the zirconia sensor. Also, at the tip of the zirconia sensor,
Stainless steel wire mesh was used as the electrode contact.

However, in such a conventional example, since the measurement gas comes into contact with the oxide film of stainless steel having a strong catalytic ability, this serves as a catalyst to oxidize the CO gas in the measurement gas, and the electromotive force of the zirconia sensor is increased. However, there is a drawback in that it lowers and causes a large measurement error.

[0005]

The present invention has been made in view of the drawbacks of the conventional example, and the technical problem to be solved is that the operation is stable, the reliability is high, and the measurement gas is high. It is an object of the present invention to provide a continuous measuring device for CO gas concentration, which can continuously and accurately measure CO gas therein.

[0006]

The feature of the present invention for solving the above-mentioned problems (technical problems) is that the zirconia solid electrolyte composed of an oxygen ion conductor is used in a continuous CO gas concentration measuring apparatus. A test tube type zirconia tube, a partition plate that divides the inner space of the zirconia tube into two chambers, an inner electrode made of a non-catalytic electrode for detecting CO gas in the measurement gas, and an outer electrode attached to the zirconia tube An outer electrode made of a porous platinum catalyst that is supplied with a reference gas,
A ring-shaped positive-side contact that contacts the lead wire of the inner electrode, and a ring-shaped negative-side contact made of a non-catalytic gold wire that contacts the lead wire of the outer electrode; The concentration of CO gas in the measurement gas is determined from the electromotive force generated between the electrode and the outer electrode.

[0007]

The present invention operates as follows. That is, the inner electrode is composed of an electrode material having an extremely small catalytic ability, and even if oxygen gas and CO gas in the measurement gas arrive together, C
Only O gas follows the Nernst equation, and C in the measurement gas
An electromotive force corresponding to the O gas concentration is generated. Further, the CO gas in the measurement gas can be continuously and accurately measured by processing the detection signal corresponding to the electromotive force with the signal processor.

[0008]

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a sectional view of the configuration of an embodiment of the present invention, in which 1 is a test tube type zirconia tube composed of a zirconia solid electrolyte made of an oxygen conductor such as stabilized zirconia, 2 is an inner electrode 16a described later. The ring-shaped positive side contact 3 that comes into contact with the lead wire of
A ring-shaped negative side contact made of a non-catalytic gold wire that comes into contact with the lead wire of b, 4 is a cover plate, and 5 is an O-ring.

Further, 16a is an inner electrode made of a non-catalytic substance attached to the bottom of the zirconia tube 1, and 16b is attached to the surface of the zirconia tube 1 in contact with the reference gas (so-called outer surface) to burn platinum powder or the like. An outer electrode made of a bonded porous platinum catalyst, 7, 7 ′ are calibration gas introduction pipes, 8 is a comparison gas introduction pipe, 9 is a thermocouple for detecting the temperature around the zirconia pipe 1, and 10 is for heating the zirconia pipe 1. Heater for 1
1 is a partition plate, 12 is a cover plate 4 and 1 is a zirconia tube.
Flange for fixing, 13 for terminal box, 14 for packing,
Reference numeral 15 is a calibration gas inlet, 16a is an inner electrode, and 16b is an outer electrode.

In the embodiment of the present invention having such a structure, the measurement gas MG is introduced into the zirconia tube 1 after the catalytic substance contained therein has been removed by passing through a filter (not shown), and then introduced into the inner electrode 16a. Is being supplied. Further, the comparative gas RG introduced from the comparative gas introduction pipe 8 is supplied to the outside of the zirconia pipe 1.

In this state, the heater 10 is used to bring the zirconia tube 1 to a temperature at which it becomes an oxygen ion derivative (usually 500).
(° C) When heated, CO contained in the measurement gas MG comes into contact with the inner electrode 16a to cause a catalytic reaction as shown in the following formula (1). CO + (1/2) O ₂ → CO ₂ ……………… (1)

As a result, the outer electrode 16 of the zirconia tube 1
An electromotive force corresponding to the amount of CO gas consumed by the reaction is generated between b and the negative contact 3. Also,
A detection signal corresponding to the electromotive force appears between the terminals E ₁ and E ₃ .

On the other hand, the O ₂ concentration of the measuring gas MG is x%, the combustible gas concentration is y%, and the O ₂ concentration of the comparative gas RG is 20.6.
When expressed as%, the electromotive force E _a can be expressed by the following equation (2) according to the Nernst equation. E _a = K _a · (RT _a / 4F) · ln (y / x) + C _a (2) where F: Faraday constant, R: gas constant, T _a : operating temperature, K _a , C _a : a constant.

Further, since the inner electrode 16a is made of an electrode material having a very small catalytic ability, even if the oxygen gas and the CO gas in the measurement gas MG arrive together, only the CO gas is expressed by the above Nernst equation. According to the measurement gas MG
An electromotive force corresponding to the gas concentration is generated. That is, the CO gas reacts with oxygen ions inside the zirconia tube 1 as CO + O ^-2 → CO ₂ + 2e (3) to generate an electromotive force. Further, by performing signal processing on the detection signal corresponding to this electromotive force by a signal processor (not shown), oxygen and CO gas in the measurement gas can be continuously and accurately measured.

On the other hand, FIG. 2 is a characteristic curve diagram of the cell electromotive force comparing the cell electromotive force generated from the zirconia sensor in the case of the conventional example and the case of the embodiment of the present invention. In this figure, the horizontal axis represents C supplied to the inner electrode 16a in FIG.
The calibration flow rate (ml / min.) With a constant O gas concentration is shown, and the vertical axis shows the electromotive force (mV) generated in the electrodes 16a and 16b of the zirconia tube 1.

Further, as is clear from the characteristic curve B in FIG. 2, in the case of the above-mentioned conventional example, the electromotive force decreases with the decrease of the calibration gas flow rate. However, in the case of the embodiment of the present invention,
As shown by the characteristic curve A, the electromotive force is constant regardless of the change in the calibration gas flow rate. The reason why such a difference occurs is as follows. That is, the zirconia tube 1 of FIG.
When the catalytic substance is present in the gas, the catalyst oxidizes the CO gas in the measurement gas into CO _{2 and} , as a result, the electromotive force of the zirconia sensor decreases. On the other hand, when no catalytic substance is present in the zirconia tube 1 of FIG. 1 as in the embodiment of the present invention, the CO gas in the measurement gas is oxidized because there is no catalytic action in the zirconia tube 1. The electromotive force of the zirconia sensor does not decrease.

The present invention is not limited to the above-mentioned embodiment, but various modifications can be made. For example, the cover plate
It may be applied to an automobile engine control or the like by removing the door 4 and the like.

[0018]

According to the present invention described in detail above, since the non-catalytic wire net made of gold wire is used as the contact, the oxide film formed on the surface does not act as a catalyst. Therefore, there is an advantage that there is no reduction in sensitivity or the difference between the calibration time and the measurement time that is caused by the catalyst in the conventional example.

[Brief description of drawings]

FIG. 1 is a structural explanatory view of an embodiment of the present invention.

FIG. 2 is a characteristic curve diagram.

[Explanation of symbols]

 1 Zirconia tube 2 Positive side contact 3 Negative side contact 4 Cover plate 5 O-ring 7,7 'Calibration gas introduction tube 8 Comparative gas introduction tube 9 Thermocouple 10 Heater 11 Partition plate 12 Flange 16a Inner electrode 16b Outer electrode

Claims (1)

[Claims] 1. A test tube-shaped zirconia tube composed of a zirconia solid electrolyte composed of an oxygen ion conductor, a partition plate for partitioning the internal space of the zirconia tube into two chambers, and a non-catalytic electrode in a measurement gas. Of the inner electrode for detecting CO gas, an outer electrode made of a porous platinum catalyst mounted on the outside of the zirconia tube and supplied with a comparative gas, and a ring-shaped positive electrode contacting the lead wire of the inner electrode. Side contact,
A ring-shaped negative side contact made of a non-catalytic gold wire that comes into contact with the lead wire of the outer electrode, and CO in the measurement gas from the electromotive force generated between the inner electrode and the outer electrode.
A continuous measuring device for CO gas concentration, which is characterized in that the gas concentration is obtained.