JPH07234203A - Nitrogen oxide sensor device - Google Patents

Abstract

PURPOSE:To measure both of NO2 and NO with high sensitivity by converting NO to NO2 in the previous stage of a flue. CONSTITUTION:From an inlet of a flue 2 through which NOx gas passes, a reducing gas catalyst 5, a converting catalyst 4 converting NO to NO2, and a nitrogen oxide sensor 3 are arranged in this order. NO2 and NO diluted with synthetic air to 5-200ppm are passed through the flue 2 at 200-1000ml/min. In this process, the catalyst 5 completely oxidizes the reducing gas if H2 and CO are used as coexistent gas, and electromotive force of the sensor 3 is measured by an electrometer without any influence of the reducing gas. In the catalyst 4, converting reaction from NO to NO2 is carried out through the catalyst put between silica wool, and NOx is detected by using a chemiluminescence type NOx. In this way, NO can be also measured with high sensitivity, while highly sensitive measurement of NOx can be carried out without being affected by coexistent gas.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nitrogen oxide sensor device for measuring NOx concentration in the atmosphere or exhaust gas of combustion equipment.

[0002]

2. Description of the Related Art Nitrogen oxide NOx emitted from combustion furnaces and automobiles is one of the causes of air pollution, and it is important to detect its concentration quickly and with high accuracy. .

Therefore, the present applicant has previously proposed a nitrogen oxide sensor having high sensitivity to NO ₂ . That is,
We have proposed electrodes that use sodium nitrite, sodium nitrate, a mixture of barium nitrate and sodium nitrate, and electrodes that have nitrite or nitrate and metal carbonate added to the electrode for low-concentration measurements. 3-275655
No. 3, Japanese Patent Application No. 3-1435).

However, these nitrogen oxide sensors are
Although it had a high sensitivity to O ₂ , but a low sensitivity to NO, it was not preferable to measure the concentration of NOx as a whole.

In view of the above problems, the present invention is NO
_{The present} invention provides a nitrogen oxide sensor device capable of measuring both ₂ and NO with high sensitivity.

[0006]

In the nitrogen oxide sensor device according to the first aspect of the present invention, a conversion catalyst for converting NO to NO ₂ is provided at the front stage of the flue, and a nitrogen oxide sensor is provided at the rear stage thereof. It is a thing.

According to a second aspect of the present invention, there is provided the nitrogen oxide sensor device according to the first aspect, wherein the nitrogen oxide sensor is a partition wall made of a material that does not allow gas to pass through the solid electrolyte piece made of a sodium ion conductor. The auxiliary phase is provided on one of the two surfaces of the solid electrolyte piece, and one of the current collectors is arranged on the auxiliary phase. The auxiliary phase is a nitrite and / or a nitrate. Of the above-mentioned carbonate or other complex salt added with oxygenate, and the other current collector is arranged so that the gas to be detected does not come into contact with the other surface of the two surfaces of this solid electrolyte piece. is there.

A nitrogen oxide sensor device according to a third aspect of the present invention is the sensor device according to the second aspect, wherein sodium carbonate or lithium carbonate is used as the metal carbonate added to the auxiliary phase. .

According to a fourth aspect of the present invention, in the nitrogen oxide sensor device according to the first to third aspects, a reducing gas catalyst is provided further upstream of the conversion catalyst in the flue.

[0010]

[Operation] The nitrogen oxide sensor device according to claim 1,
A conversion catalyst that converts NO into NO ₂ is provided in front of the nitrogen oxide sensor, and NO with low sensitivity is converted into NO ₂ . As a result, NO converted to NO ₂ can be sensed with high sensitivity.

In a nitrogen oxide sensor device according to a second aspect of the present invention, as the nitrogen oxide sensor, the surface of the solid electrolyte piece facing the outside of the tube is nitrite and / or nitrate, and metal carbonate or its by providing an auxiliary layer made of a composite salt obtained by adding an oxyacid salt other than, NO ₂
It is possible to obtain high sensitivity to. Therefore, NO
_The NO converted into ₂ can be sensed with high sensitivity.

Examples of other oxyacid salts include phosphates, silicates, borates, and sulfates.

According to the nitrogen oxide sensor device of the third aspect, high sensitivity to NO ₂ can be obtained by using such a substance.

In the nitrogen oxide sensor device according to the fourth aspect of the present invention, the reducing gas that once converts the converted NO ₂ into NO is removed by the reducing gas catalyst, and the influence of the coexisting gas is removed.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a nitrogen oxide sensor device 1 of this embodiment. This device 1 is provided with a reducing gas catalyst 5, N from a flue inlet to a flue 2 through which NOx gas passes.
A catalyst that converts O into NO ₂ (hereinafter referred to as a conversion catalyst) 4
And a nitrogen oxide sensor 3 are provided.

The detailed structure of the nitrogen oxide sensor 3 will be described with reference to FIG.

In this nitrogen oxide sensor 3, a solid electrolyte piece 12 is put on one end of a quartz glass tube 10. The periphery of the solid electrolyte piece 12 is hermetically sealed with an inorganic adhesive 13. That is, the glass tube 10 is used as a partition body that divides the solid electrolyte piece 12 into two surfaces. As the solid electrolyte piece 12, N which is a sodium ion conductor is used.
A disk-shaped sintered body of ASIC (Na ₃ Zr ₂ Si ₂ PO ₁₂ ) is used. That is, Na ₃ Po ₄ and Z
The mixed powder of rSiO ₄ and SiO ₂ was prepared by sintering at 1200 ° C. for 10 hours, and the size was 8 m.
m, thickness 0.5 mm.

After the auxiliary phase 14 was fused to the surface of the solid electrolyte piece 12 facing the outside of the glass tube 10, an Au net (100 mesh) was attached as one current collector to form a detection electrode 16. An Au wire 18 is connected to the detection electrode 16.

The surface of the solid electrolyte piece 12 facing inward of the glass tube 10 was coated with Pt black 20 and pressed by a Pt net serving as the other current collector to form an atmosphere open type counter electrode 22. An Au wire 24 is connected to the counter electrode 22.

The nitrogen oxide sensor 3 is composed of Au wire 18,
Connected to the electrometer between 24 and flowing the air diluted NOx gas only to the outside of the glass tube 10, and between the electrodes 1
The potential difference of 6,22, that is, the electromotive force ΔE (mV) is measured.

Next, the detailed structure of the conversion catalyst 4 will be described with reference to FIG.

A catalyst 32 sandwiched by quartz wool 30 is provided in the middle of the flue 2, and a gas inlet 34 to a gas outlet 3 are provided.
NOx gas is caused to flow into the nozzle 6. In the following experiment, when measuring the temperature of the conversion catalyst 4, the thermocouple 38 is used.

The results of experiments conducted to determine which material is suitable for the catalyst 32 are shown below.

The conversion catalyst 4 was screened by using a zeolite-based catalyst used in NOx selective reduction and Pt-WO ₃ .

Further, NO is 1000 p as the relative test gas.
A helium balance gas with pm and O ₂ of 10% was used.

Table 1 shows the conversion rates of NO to NO ₂ at various temperatures (250 to 400 ° C.). The left column of the table shows the substances used in the experiment.

[0028]

[Table 1] Among the various catalysts, the catalyst with the highest conversion rate was Rh-ZSM.
5 (hereinafter referred to as the first catalyst) and Pt-WO ₃ (hereinafter referred to as the first catalyst)
The second catalyst). The reaction temperature was optimized for the first catalyst and the second catalyst.
2%) was the best, and 320 ° C (71%) was the most active for the second catalyst.

(1) The results of an experiment using the nitrogen oxide sensor device 1 will be described.

The gas used is mainly synthetic air (2
1 vol% O ₂ ) and helium balance gas (21 vo)
5 to 200 ppm NO ₂ and N diluted with 1% O ₂ ).
O was used to pass through the flue 2 at 200-1000 ml / min. Then, as described above, the electromotive force of the nitrogen oxide sensor 3 was measured with an electrometer.

The reaction from NO to NO ₂ is SV5
NOx is a chemiluminescence formula N through the catalyst 32 at 000h ^−1.
It detected using the Ox meter.

Further, the oxidation of the reducing gas is performed by SV200.
The reaction was carried out at 00h ^-1 , and gases other than NOx were detected using gas chromatography.

FIG. 4 shows the result. In this figure, Δ indicates the concentration of NO ₂ , and ○ indicates the concentration of NO. Further, ● indicates the sensitivity of NO in the conventional example in which the conversion catalyst 4 and the reducing gas catalyst 5 are not used.

The graph of FIG. 4 shows that the sensitivities of NO ₂ and NO are almost the same, and that the sensitivity of NO is higher than that of the conventional example.

(2) Influence on sensitivity when various coexisting gases are contained in NOx gas H ₂ (2000 ppm), CO
(2000ppm), CH ₄ (2000ppm), CO
₂ (5%). As the conversion catalyst 4, the first catalyst having the highest activity was used. In addition, the gas to be used is mainly 5-2 diluted with synthetic air (21 vol% O ₂ ) and helium balance gas (21 vol% O ₂ ).
200-1000 using 00 ppm NO ₂ and NO
Flue 2 was passed at ml / min. Then, as described above, the electromotive force of the nitrogen oxide sensor 3 was measured with an electrometer.

When the reducing gas catalyst 5 was not provided When H ₂ and CO were used as coexisting gases, the output of the nitrogen oxide sensor 3 decreased. This is once NO ₂ on the first catalyst.
It was confirmed that even if it was converted to, part of it would return to NO due to the reaction with the reducing gas.

When the reducing gas catalyst 5 is provided In order to remove the influence of the reducing gas, the reducing gas catalyst (Pd catalyst) 5 for oxidizing the reducing gas in the preceding stage of the conversion catalyst 4 as shown in FIG. Was installed.

As a result, when H ₂ and CO are used as coexisting gases, the reducing gas catalyst 5 completely oxidizes the reducing gas, so that it is used as the nitrogen oxide sensor 3 without being affected by the reducing gas. I knew I could do it.

However, when CH ₄ was used as the reducing gas, it was affected. It is because CH ₄ is not completely oxidized by the reducing gas catalyst 5, and CH ₄ and NO ₂ are not generated on the first catalyst.
This is because it causes a reaction that NO can be generated from If CH
SV (superficial velocity) when trying to oxidize ₄ completely
Needs to be extremely small, which is not realistic when considering the cost of the Pd catalyst. Therefore, NO to NO ₂
The reaction ability is not very large, but on the catalyst CH
_The apparatus 1 using the second catalyst in which NO ₄ does not react with NO ₂ and the reducing gas catalyst 5 was used. The result is shown in FIG.

From FIG. 5, it was found that the device 1 can be used with almost no influence even when a coexisting gas is used.

According to the device 1, the NOx concentration is 100 ppm.
Up to a certain degree, N without being affected by coexisting gas
It can be measured regardless of O or NO ₂ .

Further, the oxidation reaction of the reducing gas and NO to NO
It was found that this apparatus 1 is hardly affected by water vapor, although it also includes a reaction such as a conversion reaction into ₂ , which may be affected by water vapor.

[0043]

As described above, in the nitrogen oxide sensor device of the present invention, NO can be measured with high sensitivity by providing the conversion catalyst in front of the nitrogen oxide sensor.

By providing a reducing gas catalyst further upstream of the conversion catalyst, NOx can be measured with high sensitivity without being affected by the coexisting gas.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a nitrogen oxide sensor.

FIG. 3 is an explanatory diagram of a conversion catalyst.

FIG. 4 is a state of NO ₂ and NO concentrations and their sensitivities using this apparatus.

FIG. 5 is the sensitivity of NO in the case of having a coexisting gas.

[Explanation of symbols]

 1 Nitrogen Oxide Sensor Device 2 Flue 3 Nitrogen Oxide Sensor 4 Conversion Catalyst 5 Reducing Gas Catalyst

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical indication location G01N 31/10 (72) Inventor Takatoshi Nakahira 4-1-2, Hirano-cho, Chuo-ku, Osaka-shi In Osaka Gas Co., Ltd. (72) Inventor Enomoto amount 4-1-2 Hirano-cho, Chuo-ku, Osaka City Osaka Gas Co., Ltd. (72) Inventor Tetsuo Setoguchi 4-1-2 Hirano-cho, Chuo-ku, Osaka Osaka Gas Incorporated (72) Inventor Hiroyuki Taguchi 68 Kichishoin Nitta Ninodancho, Minami-ku, Kyoto Prefecture Kyoto Prefecture Kyoto Electronics Industry Co., Ltd. (72) Inventor Shinsuke Ishihara 68 Kinoshoin Ninotancho, Minami-ku, Kyoto City, Kyoto 68 Kyoto Electronic Industry Co., Ltd.

Claims (4)

[Claims] 1. A nitrogen oxide sensor device characterized in that a conversion catalyst for converting NO to NO ₂ is provided in the preceding stage of the flue and a nitrogen oxide sensor is provided in the subsequent stage. 2. The nitrogen oxide sensor is characterized in that a solid electrolyte piece made of a sodium ion conductor is divided into two surfaces by a partition wall made of a gas impermeable material, and one of the two surfaces of the solid electrolyte piece is made. An auxiliary phase is provided, and one of the current collectors is arranged in the auxiliary phase, and the auxiliary phase is a nitrite and / or a nitrate, or a complex salt obtained by adding a metal carbonate or another oxyacid salt. 2. The nitrogen oxide sensor device according to claim 1, wherein the other of the two surfaces of the solid electrolyte piece is provided with the other current collector so that the gas to be detected does not come into contact with the other surface. . 3. The nitrogen oxide sensor device according to claim 2, wherein sodium carbonate or lithium carbonate is used as the metal carbonate added to the auxiliary phase. 4. A reducing gas catalyst is provided further upstream of the conversion catalyst in the flue.
4. The nitrogen oxide sensor device according to claim 3.