JPH04191654A - Continuously measuring method for concentration of nitrogen monoxide in gas - Google Patents

Abstract

PURPOSE:To measure continuously the concentration N2O in an exhaust gas with high precision by correcting interference by a coexistent gas by an infrared absorption analysis method. CONSTITUTION:In the case when CO2 and CO coexist in a measured gas, a CO component therein is subjected to oxidation pretreatment to be turned into CO2 under prescribed conditions, then CO2 and N2O are measured simultaneously by an infrared absorption analysis method, and N2O is corrected by using a prescribed correction formula. Correction of an N2O measured value is executed by using a correction curve prepared for each concentration of CO2, and correction curves required are lessened by the absence of combination. The curve in regard to each concentration of CO2 approximates to a straight line in a narrow range. According to this constitution, the concentration of N2O in an exhaust gas can be measured continuously with high precision by the infrared absorption analysis even when coexistent gases are present.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for continuously measuring the concentration of nitrous oxide in a gas. In particular, it relates to a method for continuous measurement of nitrous oxide in exhaust gas, for example combustion rJl gas.

[Conventional technology]

Nitrous oxide (hereinafter referred to as N20), a type of nitrogen oxide, is present in the atmosphere at a concentration of 0. 3~. It contains 0.4ppIg, and its existence has been known for a long time.

This gas, commonly called laughing gas, is used as an anesthetic in the medical field and is considered harmless to the human body at low concentrations. For this reason, not much research has been conducted on N2o.

However, with the rise in global environmental issues in recent years, N2
It has been pointed out that N2C1 acts as a global greenhouse effect and a substance that depletes the ozone layer, and in the United States, investigations have begun into the state of N2C1 emissions from fossil fuel combustion, that is, thermal power plants.

On the other hand, N20i1FI determination in exhaust gas is usually performed by gas chromatography, but depending on the sampling method, errors may occur in the Δ-j constant value, so sampling (pretreatment)
It has been reported that an effective measurement technique using the gas chromatography method has been completed ((L, J,
Muzio et al.): JAPCA.

39.287-2931.989)). However, N
In order to conduct research on countermeasure techniques for N20, it is necessary to
Since a constant value of 1 is essential and gas chromatography cannot handle this, there is a need to develop a new continuous N20 measurement technique.

A non-dispersive infrared absorption method is commonly used as a π1 device for continuous measurement of exhaust gas for SO□, NoX, etc. Recently, a prototype model of the same method was made for N20,
Research has been conducted on its performance in the United States, and the behavior of several interfering components has been reported.

[Problem to be solved by the invention]

The present invention provides a method for continuously measuring the concentration of nitrous oxide in a gas, particularly in an exhaust gas, such as a combustion exhaust gas, by correcting for interference from coexisting gases.

[Means to solve the problem]

In continuously measuring the concentration of N20 in gas, the present invention oxidizes CO in the exhaust gas containing coexistence gases such as co, co2, and other gases, converts it to CO2, and converts the N20 concentration and CO2 concentration by infrared absorption. A method for continuous measurement of the actual concentration of N20 in exhaust gas is provided, which consists of measuring by analysis and correcting the influence of the CO2 concentration.

Other coexisting gases include, for example, 02°S02 and NO. These gases have almost no effect according to the measurement method of the present invention.

In the present invention, it is preferable to measure N201 degrees using a non-dispersive infrared absorption method at a wavelength of 4.5 μm.

Furthermore, according to a preferred embodiment of the present invention, the actual concentration of N20 (ppn+) (Y) is expressed by the following formula (I).

It can be obtained by Y−aX+b (1). Here, X is an indication value obtained by infrared absorption analysis of the N20 concentration (ppo+), for example, non-dispersive infrared absorption analysis, and a and w are defined as follows.

a-Scream W7 Yu1 m-2,49 r+-2,13XiO-'b-pZ" +qZ2 +rZ+s p-5,54X10-3 q--0,220 r-1,1lX1.0-3 s-0, 610 In the above formula, Z is the indicated value obtained by infrared analysis of the CO2 (%) concentration.

In the infrared absorption method, due to the measurement principle, if the absorption wavelength of another component overlaps with the measurement wavelength of the target component, if that component is present in the measurement gas, it will be measured as the target component.

Therefore, when selecting a measurement wavelength, it is of course necessary to choose a wavelength that exhibits strong absorption in order to perform sensitive measurements, but it is also necessary to avoid overlapping absorption wavelengths of other components as much as possible. come.

FIG. 1 schematically illustrates the principle of an infrared absorption method which can also be used to carry out the method of the invention.

The infrared rays from the light source 1 pass through the sample cell 2 and comparison cell 3 (filled with N20 gas of known concentration) without being dispersed, and then pass through the main detector 6 (selectively detecting the components to be measured) and the comparative cell. It reaches a detector 7 (selectively detecting interference components).

At this time, a portion of the infrared rays passing through the sample cell 2 is absorbed by the N20 component in the sample gas introduced into the cell.

The sample gas is introduced from sample gas number 8 and taken out from outlet 9. The amount of infrared rays absorbed is detected by the detector as a difference between the amounts of infrared rays passing through each cell, measured as a gas concentration from a calibration curve, and displayed on the meter 5,
Recorded on recorder 4.

Table 1 shows the main absorption wavelengths of the absorption spectra of each component. Note that the absorption spectrum of N20 is shown in FIG. N2
0 shows strong absorption at a wavelength of 7.8 Izm or 4.5 μm, and if this wavelength is selected, sensitive measurements can be made, but at 7.871 m, S02. Hydrocarbons are 4.5p
In m, CO2.

Interference by CO is assumed.

The N20 meter used in this test has a higher measurement sensitivity of 4.5
The measurement wavelength is 7zm.

Table 1 Main absorption wavelengths by component Figure 3 shows an outline of the test equipment used to investigate the absorption of various gases. The standard gas supplied from each cylinder is adjusted and mixed to a predetermined concentration by a mass flow controller 1, and then water is removed by an electronic cooler 2, resulting in a total of 3 N2 gases.
1lpJ is determined.

The specifications of the N20 meter are as follows.

Format: Vertical VIA-5CO (manufactured by Horiba) Serial number: 15464201 Method: Non-dispersive infrared absorption method Measurement range: 0 to 50 / 250 ppm (2 range switching method) Detection section: Cell length 5CO x 1.7 mmφ: Cell material Inner surface gold plating An interference test with exhaust gas components other than N20 was conducted using the above testing apparatus.

Each coexisting gas and N20 were set to the following concentration ranges using the flue gas composition of a fluidized bed boiler as a standard.

Co220% or less [standard concentration 14%] Co
5COflf111” [11COpp ]02
20% 〃 [5%] SO□5COflp11” [50ppm]No
6COppm ” [3COppm KON20
2COppm” [11COpp]N,
Balance Note that the amount of interference of coexisting gases is defined by equation (1).

Interference amount (ppIm) - [N20 when gas coexists
Meter reading (ppm) - [N20 when no gas coexists
Meter reading (ppIll) ]・・・・・・・・・(1) (However, nitrogen always coexists.) Regarding the effects of each gas alone, first of all, CO2, Co, 02, and SO2.

Regarding NO, we investigated the interference that each individual gas has on the N20 meter.

Effects of CO2: In CO2, CO2 shows negative interference at low concentrations, but as CO2 increases, it starts to show positive interference.

Furthermore, as the N20 concentration increases, the interference shifts to the negative side as a whole, and at N20 2COppm, CO211%
Negative interference was shown in the following areas. (Table 2, Figure 4) -]〇- Table 2 CO2 interference■ Effect of CO: CO interference was negative interference, and the amount of interference increased as the CO concentration increased. Furthermore, as the N20 concentration increases, the amount of interference shifts to the negative side, and N20 2CO1
)l)m Co 5COppm showed interference of -10 ppm or more. (Table 3.

Figure 5) Effects of 02, SO2, and No: Since the amounts of interference caused by 02, SO2, and NO were all below 1 ppm, it was determined that there was no interference in this test. (
(Box 4.5.6 table below) Table 4 Interference amount of 02 - above, 111 - independent influence of each coexisting gas CO
It became clear that there was almost no effect on anything other than 2 and CO.

Effects when multiple gases coexist: Next, in order to examine the T-crossing when multiple gases coexist, 025%, SSO250pp, N
A mixed gas of 30 oppm of O was prepared, and co
2. We investigated the interference of co. (Tables 7 and 8) Table 7 CO2 interference Table 8 CO interference Co2. In both cases, the interference is the same as that when each gas exists alone, and in the measurement of the N20 component in a multicomponent gas, the interference of CO2 or CO is the same regardless of the gas component. It was found that it is possible to correct this.

Therefore, in order to understand the relationship between the indicated value of the N20 meter and the actual concentration of these gases, a graph was created with the actual concentration on the vertical axis and the indicated value of the N20 meter on the horizontal axis. Figure 6,
This is shown in Figure 7.

The graph shows a very gradual curve for each interfering gas concentration; for CO2, the curve moved to the right with increasing concentration, and for CO, it moved to the left. From this, it is easy to understand that the relationship between the indicated value of the N20 meter and the actual concentration follows a curve drawn for each concentration of CO2 or CO. Therefore, by converting the indicated value of N20 = 1 into the actual concentration, It can be seen that concentration correction i'' can be made for these interferences.

However, this correction is a supplement 1F for the case where CO2 and CO do not coexist, and since they coexist in normal actual exhaust gas, a correction method for the case where CO2 and CO coexist was studied.

The experiment was carried out using 025%, SO250pI) III,
N.

3CO1)I)fit, CO2 was added to the gas adjusted to 15%, the amount of interference was measured, and compared with the results for a gas not containing CO2 (Table 8). 9th
The table and FIG. 8 show the interaction between CO2 and CO.

If the amount of interference when CO2 and CO exist at the same time is expressed as the sum of the amounts of interference of each gas, then
The relationship between the indicated value and the actual concentration is determined for each combination of gas concentrations, and thereby the concentration of the N20 component in the actual exhaust gas can be determined.

As a result of experiments, when these gases exist at the same time,
The amount of interference was about 1 to 2 ppm lower than the value expected from the amount of interference of each gas, and although there seemed to be some kind of interaction, it was generally in agreement.

From the above, N in actual exhaust gas where CO2 and CO coexist.
It has been found that the concentration correction of 20 is possible by obtaining correction curves for combinations of CO2 and CO concentrations. An example is shown in FIG.

However, in this case, there is always an uncorrectable error of about 1 to 2 ppffl, and a correction curve is required for each combination of CO2 and CO concentrations.
If the concentration of Co changes at the same time, a large number of correction curves will be required, resulting in problems such as difficulty in use.

Therefore, we devised and considered a new correction method as follows.

That is, the CO acid component CO2 in the measurement gas is pre-oxidized and corrected as CO2.

In this method, since correction is performed using a correction curve (FIG. 6) prepared for each CO2 concentration, the above-mentioned error is eliminated, and the number of correction curves required is only the number of fractions without any combination. In this case, the curve at each CO2 concentration draws an extremely gentle arc, and can be approximated as a straight line within a narrow concentration range.

Table 10 and FIG. 10 show coefficients a and b when each curve is approximated to a straight line equation Y-aX+b in the range of N20 concentration from 0 to 150 ppm.

Table 10 CO2 coefficient a, b From this, it can be seen that a and b are each curved as shown in FIG.

Therefore, depending on the concentration of CO2, find the values of a and b, create a straight line equation Y-aX+b, and add to this the indicated value of the N20 meter "
This means that the N20 concentration can be corrected by applying X''.

By the above method, it is possible to continuously measure the N20R degree with an accuracy of ±0.5 ppm.

Continuous measurement system for N20 According to the present invention, for example, continuous measurement of N20 in boiler exhaust gas can be performed as follows.

After CO in exhaust gas is pre-treated to oxidize to CO2, CO2 and N20 are measured simultaneously and corrected using a correction formula.

For example, CO oxidation pretreatment can be carried out using Nissan Girdler Catalyst [
When Bobkalai IN-220J is used, CO oxidation treatment is possible under the following conditions. (In effect, 1
CO% becomes CO2. ) Temperature>130℃ superficial velocity<7, CO0h-1 CO concentration<1. ．． CO01) pHl As described above, according to the present invention, the gas that interferes with the measurement of N20 by non-dispersive infrared absorption method at a wavelength of 4.5 μm is CO01) pHl.
□ and CO available 02. SO2°No rarely interferes.

■ CO2 shows negative interference when the concentration of CO□ is low, and positive interference when the concentration of CO2 is high. In addition, CO shows negative interference, and the degree of interference for both CO2 and CO is N2
0 varies depending on the concentration.

■ Even under boiler exhaust gas conditions (multiple gas coexistence),
The interference components are only CO2 and CO, and it is possible to correct the N20 measurement value from the relationship between them.

■ As a correction method, considering that correction using both CO2 and CO components is waste and is inconvenient, and CO can be oxidized relatively easily, CO is pre-oxidized and converted to all CO2. Make corrections.

■ Therefore, after pre-oxidizing CO2 and N20
By simultaneously measuring N20 and correcting N20 using a correction formula, it became possible to continuously measure the N20 concentration with an accuracy of ±0.5 ppI11.

〔Effect of the invention〕

According to the present invention, in the measurement of nitrous oxide (N20) concentration in exhaust gas, in the presence of coexisting gas,
Furthermore, maintenance is easy, and continuous 11111 measurement is possible with high precision, making it particularly useful as an industrial measuring method.

[Brief explanation of the drawing]

FIG. 1 is a schematic illustration showing the principle of the infrared absorption method. FIG. 2 is a non-dispersive infrared absorption spectrum of N20. FIG. 3 is a schematic diagram of a test apparatus for investigating the absorption of various gases. FIG. 4 is a graph showing the interference of CO2 with N20 measurements. FIG. 5 is a graph showing the interference of CO with N20 measurements. FIG. 6 is a graph showing the relationship between the indicated value of the N20 meter and the actual concentration of N20 when CO2 is changed. FIG. 7 is a graph showing the relationship between the indicated value of the N20 meter and the actual concentration of N20 when CO is varied. FIG. 8 is a graph showing interference with N20 measurements when CO2 is fixed at 15% and the CO content is varied. Figure 9 shows the relationship between the N20 meter reading and the actual concentration of N20 (
It is a graph showing CO correction in the case of CO2 15%. FIG. 10 is a graph showing coefficients a and b. [Explanation of main symbols] Figure 1: 1...Light source, 2...Sample cell, 3...Comparison cell,
4... Recorder, 5... Meter, 6... Main detector, 7... Comparative detector, 8... Sample gas population, 9... Sample gas outlet. Figure 3: 1...Mass flow controller, 2...Electronic cooler, 3...N20 meter. Applicant's agent Hiroshi Fujimoto Figure 1

Claims (1)

[Claims] 1. In the exhaust gas containing N_2O, CO, CO_2, and other coexisting gases, CO is oxidized and converted to CO_2, and the N_2O concentration and CO_2 concentration are measured by infrared absorption analysis to determine the CO_2 concentration. A method for continuously measuring the actual concentration of N_2O in exhaust gas, characterized by correcting the influence of. 2.O_2, SO_2 and NO as other coexisting gases
2. The method of claim 1. 3. The method according to claim 2 or 3, wherein the N_2O concentration is measured by a non-dispersive infrared absorption method at a wavelength of 4.5 μm. 4. The actual concentration (ppm) (Y) of N_2O is calculated using the following formula (I
), Y=aX+b(I) [wherein,
There are tables etc.▼ m=2.49 n=2.13×10^-^4 b=pZ^3+qZ2+rZ+s p=5.54×10^-^3 q=-0.220 r=1.11×10 ^-^3 s=0.610 Z is the indicated value obtained by infrared analysis of CO_2 (%) concentration. ] The method according to any one of claims 1 to 3, obtained by: