JPH049754A - Apparatus for continuously measuring concentration of gas - Google Patents

Abstract

PURPOSE:To accurately measure the concn. of gas by using the gold paste film baked to the surface of a zirconia solid electrolyte as the electrode lead of the electrode on a measuring side mounted on a zirconia sensor. CONSTITUTION:The first and second inside leads 14a, 14b of a zirconia sensor constituted of a zirconia solid electrolyte composed of an oxygen ion conductive body are constituted of films formed by baking gold paste. Since gold has no catalytic action, the combustion gas (e.g., CO) in gas MG to be measured is not oxidized by the electrode leads 14a, 14b and the electromotive force of the sensor is not lowered. The MG is supplied into the electrolyte 6 by diffusion or convection and the flow rate of the supplied MG is little but the electromotive force of the sensor is not lowered by the reduction of the flow rate of the MG. That is, by using the gold paste films as the electrode leads, it can be avoided that a large error is generated by the oxidation of the combustion gas component in the MG.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a continuous measuring device for gas concentration, and more specifically, the present invention relates to a device for continuously measuring gas concentration. The present invention relates to a continuous gas concentration measuring device that is capable of continuously and accurately measuring the temperature of a desired gas contained in the measurement gas even when the gas concentration is measured.

<Conventional technology> In general, in the combustion process, the concentration of combustible gases (such as Go) and oxygen contained in the flue gas flowing through the flue is constantly monitored to ensure that the combustion furnace is operated in an optimal state from the viewpoint of energy conservation and pollution prevention. Combustion is controlled so that Conventionally, the concentration of oxygen and combustible gas contained in the combustion exhaust gas flowing through the flue can be continuously measured in the following manner. That is, oxygen in the sample gas is measured with a zirconia oxygen meter,
The combustible gas in the measured gas was analyzed using a separate analyzer, such as an infrared gas analyzer.

However, in such a conventional example (hereinafter referred to as the "first conventional example"), the measurement points are separate, and the measurement gas is sampled from the same measurement point with one measuring device. The disadvantage is that the measurement accuracy is lower than when the method is used. In addition, since two measuring devices are used,
Another drawback was that the construction and maintenance costs were approximately twice as high as those when using a single measuring device.

Having developed a continuous gas concentration measuring device that eliminates the drawbacks of the first conventional example, the applicant of the present application filed a patent application entitled "Continuous Gas Concentration Measuring Device" on March 30, 1990 (
(Application number and publication number have not yet been determined). The continuous gas concentration measuring device (hereinafter referred to as "second conventional example") according to the present invention includes a test tube-shaped zirconia solid electrolyte made of a zirconia solid electrolyte made of an oxygen ion conductor, and a test tube-shaped zirconia solid electrolyte made of a zirconia solid electrolyte. A partition plate that technically partitions the internal space, a first inner electrode that is a non-catalytic electrode that detects combustible gas in the measurement gas, and a platinum with strong catalytic ability; a camellia that detects oxygen in the measurement gas. a second inner electrode;
an outer electrode made of a porous platinum catalyst mounted on the outside of the zirconia solid electrolyte and to which a reference gas is supplied;
Determining the concentration of combustible gas in the measurement gas from the electromotive force generated between the inner electrode and the outer electrode, and determining the oxygen gas concentration in the measurement gas from the electromotive force generated between the second inner electrode and the outer electrode. It is characterized by:

However, in such a second conventional example, the first and second inner fIl! A baked platinum vest is used as the electrode lead of the Is electrode. Therefore, the electrode lead acts as a catalyst and the combustible gas in the measurement gas is oxidized.
As a result, the electromotive force of the zirconia sensor decreases, resulting in a large measurement error.

<Problems to be Solved by the Invention> The present invention has been made in view of the drawbacks of the second conventional example, and the technical problem to be solved is that the electrode lead of the zirconia sensor acts as a catalyst and the measurement gas It is an object of the present invention to provide a continuous gas concentration measuring device configured to avoid the occurrence of large errors due to oxidation of combustible gas components therein.

A feature of the present invention that solves the above-mentioned problems (technical problems) is the origin of a zirconia sensor composed of a zirconia solid electrolyte made of an oxygen ion conductor. In a continuous gas concentration measuring device that determines the combustible gas concentration in the measurement gas from electric power, a gold paste film baked on the surface of the zirconia solid electrolyte is attached to the S' [i-lead] of the measurement electrode attached to the zirconia sensor. The reason is that

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a cross-sectional view of the configuration of an embodiment of the present invention, and in the figure,
1 is the wall of the flue through which the measurement gas MG such as combustion exhaust gas flows, 2 is the casing, 3 is a flange for fixing the zirconia solid electrolyte 6, which will be described later, to the casing 2, 4 is the O-ring, and 5 is the ceramic adhesive for insulation. 6 is a test tube-shaped zirconia solid electrolyte made of an O'2 conductor such as stabilized zirconia, 7 is a partition plate, and 8a is a first inner electrode 10a to be described later.
a ring-shaped first contact I, which contacts the electrode lead of
8b is the second inner ry! A link-shaped second contact contacts the electrode lead of the J electrode 10b, 9 is a heater for heating the zirconia solid electrolyte 6, and 10a is a non-catalytic (
Z)'MO208(
a first inner electrode, which is a non-catalytic electrode such as molybdenum zirconium oxide) and detects a combustible gas;
The second inner II is made of an electrode with strong catalytic ability to detect oxygen!
II electrode, 11 is a zirconia solid electrolyte 6 is a reference gas R
The outer 1III electrode is attached to the surface (outer surface) in contact with G and is made of a porous platinum catalyst made by sintering platinum powder, etc., 12 is a reference gas introduction tube, ] 3 is a lid wire of the second inner electric camellia 10b, which is attached to the flange. This is a platinum wire connected to 3.

Further, FIG. 2 is an enlarged cross-sectional view of the essential parts of the zirconia sensor, and in the figure, the same symbols as in FIG. 1 are used with the same meanings, and repeated explanations will be omitted here.

In addition, 1.4a and 14b are first and second inner leads made of a film formed by applying gold paste at room temperature and baking it at a temperature of about 750 to 900°C, and 15 is a platinum base I. The outer lid is made of a film that has been baked with.

In the embodiment of the present invention having such a configuration, the measurement gas MG is guided inside the zirconia solid electrolyte-6, and the first inner electrode 10a and the second inner electrode 11! are separated by the partition plate 7. 11 electrodes 1. It is supplied to Ob. Also,
A reference gas RG introduced from a reference gas introduction pipe 12 is supplied to the outside of the zirconia solid electrolyte 6. In this state, when the zirconia solid electrolyte 6 is heated by the heater 9 to a temperature at which it becomes an oxygen ion derivative (usually 500" C), combustible gas components such as CO contained in the measurement gas MG are transferred to the first inner electrode 10a. Upon contact, a catalytic reaction as shown in the following formula (1) occurs.

CO+(1,/2)02-CO2--<1) As a result, there is a residual amount between the second inner a1=pole of the zirconia sensor and the second contact 8b after subtracting the oxygen consumed by the reaction. An electromotive force is generated corresponding to the amount of oxygen. Further, a detection signal corresponding to the electromotive force is sent to terminal E2. E
'It will rain between x.

On the other hand, when the 02A degree of the measurement gas MG is χ%, the combustible gas concentration is y%, and the 02 concentration of the reference gas RG is 20°6%, the electromotive force EA is calculated as shown in the following equation (2) according to Nernst's formula. can be expressed.

EA=Ka・(RTA/4F)・lx [20°6
/fl'(1/2>・&l]+CA---(2) However, F: Faraday constant, R: gas constant, 1゛A: operating temperature, KA, CA: constant.

Moreover, since the first inner electrode 10a is constituted by an electrode film with extremely low catalytic ability, even if the oxygen gas and combustible gas in the measurement gas MG arrive together, the combustible gas alone or the According to the formula, the oxygen partial pressure in the measurement gas MG (
20.6%) and the oxygen partial pressure of the reference gas RG. That is, combustible gases (e.g. CO
) is the 0-2 ion inside the zirconia solid electrolyte and Co
10' →CO2+ 2 e-・--
-(:3) It reacts and generates an electromotive force. Further, a detection signal corresponding to this electromotive force is applied between terminals E+ and E':a.

Therefore, the detection signal detected between the terminals El and E3 and the terminal E2. By processing the detection signal detected between E3 with a signal processor (not shown), it becomes possible to continuously and accurately measure oxygen and combustible gas in the measurement gas.

On the other hand, FIG. 3 shows the first and second inner leads 1.4a.
, 14b is an experimental result comparing the cell electromotive force generated from a zirconia sensor in the case of a so-called gold lead made of a film with baked gold paste and the case of a so-called platinum lead made of a film with baked platinum paste. FIG. 1 is a chart showing characteristics of cell electromotive force. In this figure, the horizontal axis indicates the flow J of the calibration gas whose combustible gas concentration and oxygen gas concentration are constant, which is supplied to the first and second inner leads 14a and 14b in FIG.
i (ml/min, ), and the vertical axis represents the electromotive force (mV) generated between the electrodes of the zirconia sensor. Also, as is clear from Figure 3, in the case of platinum leads, the cell electromotive force changes as the calibration gas flow rate decreases, and in the case of gold leads, the cell electromotive force increases regardless of changes in the calibration gas meteor. It remains constant. This is due to the following reasons.

That is, when the first and second inner leads 14a and '14b of FIG. 1 are platinum leads made of a film baked with platinum paste 1- as in the second conventional example, the electrode leads acts as a catalyst to reduce combustible gas (e.g. C) in the measurement gas.
O) is oxidized and becomes peroxidized! T! l (e.g. C02)
As a result, the electromotive force of the zirconia sensor decreases. On the other hand, as in the embodiment of the present invention, the first
In the case where the first and second inner leads 14a and 14b in the figure are gold leads made of a film of baked gold paste, gold does not have a catalytic effect like platinum, so the electrode leads can The combustible gas is not oxidized and the electromotive force of the zirconia sensor is not reduced. .

In addition, when actually measuring the measurement gas, the measurement gas is supplied by diffusion or convection into the zirconia surrounding electrolyte 6 shown in Fig. 1, and the flow rate of the supplied gas is small. This phenomenon becomes more noticeable.

Note that the present invention is not limited to the above-described embodiments, and can be modified in various ways. For example, the leads 14a and 14b may be attached to the zirconia solid electrolyte 14 first and then overlapped with a portion of these leads. 1 and the second electrode 10a, 10.
b may be attached to the zirconia solid electrolyte 14. Alternatively, there may be two separate zirconia sensors, the first zirconia sensor being a conventional oxygen sensor, and the second zirconia sensor having a non-catalytic electrode and using a film of baked gold base as the electrode lead. good.

<Effects of the Invention> According to the present invention as described in detail above, the combustible gas concentration in the measurement gas is determined from the electromotive force of a zirconia sensor made of a zirconia solid electrolyte made of an oxygen ion conductor. In the measuring device, a gold base l-1 baked on the surface of the zirconia solid electrolyte
10 was configured to serve as an electrode lead of a measurement side electrode attached to the zirconia sensor. Gold has excellent corrosion resistance and does not have catalytic properties like platinum, so the electrode lead of the zirconia sensor acts as a catalyst to avoid oxidation of combustible gas components in the measurement gas, which ultimately causes large errors. Become. In addition, since it is possible to accurately measure 02a degrees and combustible gas concentration in the presence of flammable gases, it can be applied to a wide range of combustion equipment such as engine controls for automobiles and aircraft, and furthermore to sensors for living environments such as CO gas sensors. It becomes possible to apply it.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of the configuration of an embodiment of the present invention, FIG. 2C is an enlarged cross-sectional view of a Zirnia sensor, and FIG. 3 is a zirconia cell electromotive force characteristic curve. DESCRIPTION OF SYMBOLS 1... Flue wall, 2... Casing, 3... Flange, 4... O-ring, 5... Ceramic adhesive, 6... Zirconia solid electrolyte, 7...・Partition plate,
8a8b... Contact, 9... Heater, 1, 0
a-...First inner side @g;,,10 b-...Second inner side a
+ t i, 11...Outer electrode, 12...Reference gas introduction tube, 13...Platinum wire, 14a, 14b...
Inner lead-I4.15...Outer lead Figure 1 Figure 3

Claims (1)

[Scope of Claims] 1) A continuous gas concentration measuring device that determines the combustible gas concentration in the measurement gas from the electromotive force of a zirconia sensor made of a zirconia solid electrolyte made of an oxygen ion conductor. A continuous measuring device for gas concentration, characterized in that a gold paste film baked on the surface is used as an electrode lead of a measuring electrode attached to the zirconia sensor. 2) A test tube-shaped zirconia solid electrolyte composed of a zirconia solid electrolyte made of an oxygen ion conductor
The measurement side electrode of the first zirconia sensor is composed of an electrode with strong catalytic ability to detect oxygen in the measurement gas, and the measurement side electrode of the second zirconia sensor is a non-catalytic electrode, In a continuous gas concentration measuring device, the concentration of oxygen gas in the measurement gas is determined from the electromotive force of the first zirconia sensor, and the combustible gas concentration in the measurement gas is determined from the electromotive force of the first and second zirconia sensors. . A continuous gas concentration measuring device, characterized in that a film on which gold paste is baked is used as an electrode lead of a measuring electrode attached to the second zirconia sensor.