JPH06123682A - Device for measuring nox concentration - Google Patents

Abstract

PURPOSE:To provide a device for measuring NOx concentration which can measure a NOx concentration in a gas even if NO2 concentration ratio is high. CONSTITUTION:In the device used when NO2 concentration ratio is high as in a waste gas from a diesel engine, a chemical plant, etc., a sampling probe 1 for sucking a gas sample, a first NOx converter 3 for converting NO2 to NO, a dehumidifier 5, a second NOx converter 6, and a chemiluminescence NOx analyzer 7 are connected in this order with a duct 2 and a heater consisting of Mo wire coil is built in the duct 2 at least between the first NOx converter 3 and the dehumidifier 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is an apparatus for measuring the concentration of total nitrogen oxides (NO _x ) in gas when the ratio of NO ₂ is high, such as exhaust gas from diesel engines and chemical plants. It is about.

[0002]

2. Description of the Related Art Total nitrogen oxides (N
As a method for measuring the concentration of O _x ) (NO + NO ₂ ), PDS is used.
The method (JIS K0104) and the like are defined as the JIS method, and as the instrumental analysis method, the chemiluminescence method (the chemirumi method) is also adopted in JIS B7982. This instrumental analysis method can accurately measure the NO concentration when the ratio of NO ₂ is low, the concentration of NO is low, and the concentration of coexisting oxygen is low, as in the case of boiler exhaust gas. It should be noted that this chemiluminescence method originally measures NO, and when the NO _x concentration is required, the NO _x converter converts NO ₂ into NO.
After converting into NO, the NO _x concentration was measured by measuring the total NO.

[0003]

[Problems to be Solved by the Invention] The NO _x concentration measuring method of the prior art is used as it is, as in the case of diesel engine exhaust gas.
If applied when the ratio of O ₂ is high, there are the following problems. When the concentration and ratio of NO ₂ are high, NO ₂ is dissolved in the dehumidified water in the pretreatment process for removing the water, which has a negative effect. When the concentration of NO, O ₂ is high, it reacts between sampling and measurement to generate NO ₂ , which has a negative influence on the measured value.

The present invention solves the problems of the conventional NO _x concentration measuring method described above when NO ₂ is high such as exhaust gas from a diesel engine, a chemical plant, etc., and continuously and easily NO _x in gas. It is an object of the present invention to provide a device capable of measuring the concentration.

[0005]

[Means for Solving the Problems] NO ₂ during sampling
In order to prevent water from being removed along with the drainage of water in the gas, measures should be taken to ensure that the sampling pipeline is kept warm, and NO ₂ is added in the middle of the sampling pipeline.
The first NO _x converter that converts to molybdenum is installed, and molybdenum (M _O ) is provided in the sampling line after the converter.
Put the wire coil and heat. The NO ₂ component in the gas measured by this measure is converted to N by the NO _x converter.
O is changed to, by reaction with subsequent coexisting oxygen, NO ₂ generated in the sampling conduit is suppressed to a minimum by the catalytic effect of M _O coil in the conduit. In this way, the NO ₂ component in the gas is all cooled to NO, and the gas is drained to remove moisture from the gas. Then the second N
The NO concentration is measured by a chemiluminescence method (chemylmi method) via an O _x converter.

[0006]

By converting NO ₂ in the gas sampling into NO by the first NO _x converter, NO ₂ is prevented from reacting with water in the gas to become LHNO ₃ and discharged together with the drain. The heating device including the coil of the _MO wire prevents NO in the pipe from reacting with residual oxygen in the gas to change NO into NO ₂ , by a catalytic effect.

After dehumidifying the gas, it is further passed through a NO _x converter, and all the remaining NO ₂ is converted to NO.
O analyzer (a NO analyzer based on chemiluminescence is used to measure the amount of NO in the gas. By keeping the sampling pipe warm, the change from NO to NO ₂ is prevented.

[0008]

Embodiments of the present invention will be described with reference to FIGS. In FIG. 1, a gas sample is sampled by a sampling probe 1 and is passed through a pipe 2 which is kept warm and is provided with a drain prevention measure, and then a first NO _x converter 3
Will be introduced to. Details of this NO _x converter 3 are shown in FIG.
As shown in FIG. 5, a large number of nets, which are molybdenum (M 2 _O ) wires 9, are installed so that the temperature can be adjusted to a constant temperature, and NO ₂ is converted to NO by the action of the M 2 _O catalyst.

NO in the gas sample₂Is converted to NO
The gas is M_OVia line 4 loaded with wire coil 9 '
Therefore, the dehumidifier 5 removes water. After this dehumidifier 5
Second NO_xThe converter 6 and the chemirumi NO analyzer 7
It is a commercially available product that is generally used, and its analysis value (NO
Record the density with a recorder 8. With the device of the present invention described above
NO₂Accurate NO even for gas samples containing a lot of _x
It is possible to measure the concentration. Moisture in the gas drains
When converting to NO, NO₂Is present, the following equation (1)
The reaction shown is performed and NO_xThe concentration is reduced.

4NO₂+ 2H₂O + O₂→ 4HNO₃ ………… (1) Furthermore, NO concentration, O₂When the concentration is high, it is shown by the formula (2).
Reaction is performed, NO ₂Is generated. 2NO + O₂→ 2 NO₂ ………… (2) Minimize the reactions shown in the above reaction formulas (1) and (2).
And NO_xIf all is set to NO by the converter, it will be correct
It is possible to make good measurements.

[0011] According to the present invention, thus the total nitrogen oxides concentration of NO _x via the NO gas can be accurately measured. The following reaction formula (3) shows the reaction in the NO _x converter. M _O catalyst _{2NO 2 → 2NO + O 2 ............} (3) NO x value measured in the present invention, as shown in the following Table 1,
It is almost in agreement with the wet manual analysis (PDS method), and it can be seen that accurate measurement can be performed.

[0012]

[Table 1]

[0013]

The NO _x concentration measuring device according to the present invention comprises:
Sampling probe for sucking gas sample and NO ₂
A first NO _x converter for converting NO to NO, a dehumidifier,
The second NO _x converter and the chemilumine NO _x analyzer are connected by a pipe line in the above-mentioned order, and a heating device consisting of a coil of M _O wire is provided at least in the pipe line between the first NO _x converter and the dehumidifier. The interior has the following effects.

To accurately measure the concentration of total nitrogen oxides (NO _x ) in a diesel engine or chemical plant where the content ratio of nitrogen dioxide (NO ₂ ) is high, without being affected by the sampling system. You can

[Brief description of drawings]

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

FIG. 2 is a configuration diagram of the NO _x converter shown in FIG. 1.

[Explanation of symbols]

1 Sampling probe 2 Pipe line 3 First NO _x converter 4 Pipe line 5 Dehumidifier 6 Second NO _x converter 7 Chemirumi NO analyzer 8 Recorder

Claims (1)

[Claims] 1. From a diesel engine, chemical plant, etc.
NO as exhaust gas ₂N used when the content ratio of N is high
O_xIn the concentration measuring device,
Sampling probe and NO₂First N to convert NO to NO
O_xConverter, dehumidifier, second NO_xconverter
And chemirumi no_xConnect the analyzer with the pipeline in the above order.
Connected, at least the first NO_xBetween converter and dehumidifier
To the pipeline of_OIt is equipped with a heating device consisting of a wire coil.
NO characterized by_xConcentration measuring device.