JPS584303B2 - Filter for removing interfering gas in carbon monoxide analyzer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a carbon monoxide analyzer, and particularly to an interference gas removal filter for eliminating analysis errors caused by harmful gases in a flue gas measuring instrument.

Currently, the devices widely used as carbon monoxide analyzers include large types such as infrared spectrophotometers and gas chromatography, but simpler and more portable types use catalysts such as hopcalite or platinum. One uses the combustion heat generated by catalytic oxidation of carbon monoxide, the other uses the change in thermal conductivity after converting it to carbon dioxide, or the one uses the change in the electrical resistance of the absorption liquid. There are also known methods that utilize changes in surface potential due to the adsorption of carbon monoxide onto the surface of a metal oxide semiconductor.

These methods, especially when applied to the measurement of flue gases, can be used to detect significant differences between nitrogen monoxide and nitrogen dioxide, which have similar physical and chemical properties to carbon monoxide in terms of electronic structure and physical properties. be protected from damage.

When the purpose is to measure carbon monoxide at 100 ppm in combustion exhaust gas, etc., normally, in such a system, 100 ppm
Since some nitrogen oxides also coexist, the measured values are significantly interfered with, making it impossible to measure them at all.

Therefore, in order to avoid interference with this nitrogen oxide NOx,
A filter is required to remove NOx.

Conventionally, this type of filter has been manufactured using a dry method using an adsorbent such as activated carbon, molecular sheep, or silica gel, or a wet method using an alkali chlorite aqueous solution or an alkali permanganate aqueous solution. Various attempts have been made, but all of them involve many technical problems and have not been put into practical use.

First of all, it is a wet method, but since it uses a liquid, it loses the advantage of being easy to carry, which is a characteristic of the portability of analytical instruments, and it is highly corrosive because it bubbles gas in an aqueous solution. There were problems such as strong mist scattering and contaminating the sampling channel.

Regarding the dry method, most of the NOx in the flue gas (
Nitric oxide (No), which accounts for 80 to 90% or more, could hardly be removed and was of no use.

On the other hand, as a compromise between the two, a method has been attempted in which the above-mentioned aqueous solution is contained in a porous carrier together with a wetting agent such as ethylene glycol, but in the case of a filter with this configuration,
Although the initial performance was excellent, the service life was short and the filter had to be replaced frequently, which was a maintenance problem.

The filter of the present invention is provided in the gas suction sampling channel of a carbon monoxide analyzer, and is naturally used as a filter for removing interfering gases, so it is provided upstream of the analysis section.

Depending on the type of analyzer, a water vapor trap may be required, or a dust removal device may be required, but since the analyzer of the present invention uses a chemical absorbent, there is no risk of performance deterioration due to clogging. It is preferable to provide these filters in the flow path in front of this filter in order to prevent this and also to prevent the concern that components may dissolve due to moisture absorption.

In a normal portable carbon monoxide analyzer, the gas sampling flow rate is about 0.1 to 2 l/min, and 100 pp
In the case of NOx treatment at the m level, a filter with a capacity of about 500 ml can be used to obtain a life of 2000 to 40000 hours.

Although this is a disposable type, it has a sufficiently long life as a filter used in an analytical device.

The filter of the present invention removes NOx through a chemisorption reaction as shown in the following example.

1 Reaction between chlorite and NO in the presence of alkali 4NO+3NaClO2+4NaOH→4NaNO3+
3NaCl+2H2O2 Reaction between permanganate and NONO+KMnO4→KNO3+MnO2 3 Reaction between alkali and NO2 2NO2+K2CO3→KNO3+KNO2+CO2 All of the above reactions are liquid phase reactions, but in the case of the present invention, the surface of the kneaded and granulated product is It is thought that this is due to an extremely complex chemical reaction involving solid-liquid-gas.

A feature of the present invention is that by combining two types of composition systems, NOx contained in flue gas and which interferes with carbon monoxide analysis is almost completely removed, and it does not react with carbon monoxide itself. It is.

The first composition is composed of an alkali metal chlorite or permanganate, an alkali, and a cured product made of a cement material.

This cured product can be produced by granulating and molding a kneaded product with water.

When comparing chlorite and permanganate, the former has better granulation properties and is easier to handle.

Examples of alkali include NaOH, KOH, Na2CO3, K2CO3, Ca(OH)2, Mg(O
H) 2 etc. can be applied.

Of these, Ca(OH)2 also has a function as a cement material, especially the ClO2 produced when chlorite decomposes.
It is suitable for combination with chlorite as it absorbs and fixes chlorite.

Cement materials include bentonite, alumina cement,
Alumina sol, silica sol, diatomaceous earth, clay, calcined gypsum (calcium sulfate), Portland cement, aluminum phosphate, kaolin, water glass, etc. can be used.

The second composition is characterized by using powdered activated carbon instead of chlorite and permanganate.

As the alkali and cement material, the same ones as in the first composition can be used.

The first composition has particularly excellent ability to remove NOx.

However, since this is an oxidation absorption method, depending on the operating conditions, N
Although O is oxidized to NO2, NO2 may not be completely absorbed and may be emitted.

The second composition has excellent NO2 removal ability and
2 is removed by almost 100%.

The NOx absorption reaction by alkali is the NOx absorption reaction shown earlier.
In addition to the reaction with 2, there is also a reaction with N2O3, and the reaction rate of the latter is faster.

On the other hand, activated carbon has the property of reducing NO2 and adsorbing it as N2O3.
3 and this is absorbed by alkali, so NO
It seems that 2 can be removed efficiently.

As the alkali to be combined with this activated carbon, Ca(OH)2 and K2CO3 having low solubility, such as Ca(NO2)2 and Ca(NO3)2, which are absorption reaction products, are suitable.

The first and second compositions may be combined in a filter configuration in which a packed layer of the first composition is provided on the upstream side of the sampling channel, and a packed layer of the second composition is provided on the downstream side.

This causes NO and N to interfere with carbon monoxide analysis.
O2 can be almost completely removed.

In addition, the chlorite and potassium permanganate in the first composition are oxidizing agents, while the activated carbon in the second composition is a reducing agent, so when the two come into contact, the activated carbon burns, and in some cases There is a risk of explosion, but since these are separately cured products, there is no such risk.

Next, embodiments of the present invention will be described.

NaClO2, Ca(OH)2 and C as the first composition
A mixture of aSO4.1/2H2O in a weight ratio of 4/3/3, and a second composition of K2CO3 and Ca.
The raw material is a mixture of (OH)2, CaSO4・1/2H2O, and activated carbon powder in a weight ratio of 3/3/2/2, each of which is kneaded with water, extruded into a columnar shape, and dried. The particles having a particle size of 4 to 8 mesh were used after being hardened and then ground.

Collect 5 ml of each of these and place them in a cylindrical container with a diameter of 20 mm, with the first composition in the front stream and the second composition in the back stream.
Filled with a composition of
It was led to an Ox analyzer and the NOx concentration was analyzed.

Further, NO gas was added to this combustion exhaust gas from a cylinder to create a gas with even higher concentration, and the NOx concentration on the filter outlet side was also analyzed.

The results of these experiments are shown in the figure. As can be seen from the figure, over a considerable NOx concentration range, the NOx concentration is close to 100%.
x removal characteristics.

Here, the combustion equipment used as the NOx source was a stove, and its NOx concentration was 22.5 ppm, of which NO was 18.
．． It was 2 ppm.

Due to such performance, the filter of the present invention can almost completely overcome the influence of NOx interference as an interference gas removal filter for a portable carbon monoxide analyzer.

Note that one feature of this filter is that it is fully functional at room temperature.

However, when using chlorite, there is a concern that it will thermally decompose.

NaCl02→NaCl+O2 The temperature dependence of this decomposition reaction is NaClO2/Ca(OH
) It has been confirmed that a composition with a ratio of 2/CaSO4.1/2H2O of 4/3/3 is stable for 10,000 hours at 80°C.

Even if the filter layer temperature increases during normal use, the
Since it is thought that the temperature will not exceed 0.degree. C., there is no need for troublesome temperature control of the filter packed bed when using the filter, making it possible to construct an extremely simple flow path.

[Brief explanation of the drawing]

The drawings show various types of filters used in one embodiment of the present invention.
It shows the NOx removal rate versus x concentration.

Claims (1)

[Claims] 1. A first composition consisting of a cured product composed of an alkali metal chlorite or permanganate, an alkali, and a cement material is placed in the gas sampling channel of a carbon monoxide analyzer. 1. A filter for removing interfering gas from a carbon monoxide analyzer, characterized in that the filter is filled with a second composition consisting of a hardened material composed of an alkali, a cement material, and powdered activated carbon. 2. Claim 1, wherein the first composition comprises sodium chlorite, calcium hydroxide and cement material, and the alkali of the second composition is selected from the group of potassium carbonate and calcium hydroxide. Interfering gas removal filter for carbon monoxide analyzer as described in . 3. A filter for removing interfering gas from a carbon monoxide analyzer according to claim 2, wherein the cement material of the first and second compositions is calcium sulfate.