JPS598772B2 - Ammonia gas analyzer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention instantly and directly measures the ammonia gas concentration in the flue gas of a denitrification plant or a desulfurization plant.
This article relates to an ammonia gas analyzer using a dispersive ultraviolet absorption method that performs continuous automatic measurements.

Coupled with the environmental administration's NOx regulations, the full-scale, large-scale use of denitrification plants is fast approaching.

The mainstream method for denitration is a dry denitration method that uses ammonia to reduce NOx to water and nitrogen. This denitrification method releases excess ammonia into the atmosphere, causing new air pollution. Furthermore, excessive release of ammonia results in the use of a large amount of ammonia, leading to an increase in the operating cost of the denitrification equipment.
Therefore, from the standpoint of pollution prevention, it is necessary to constantly monitor leakage and ammonia. There is also a strong intention to keep ammonia consumption low by controlling the amount of ammonia injection while monitoring leak ammonia. Under these circumstances, the demand for automatic ammonia measuring instruments in flue gas has increased. Conventional automatic ammonia measuring instruments include those that employ the solution conductivity method, those that are based on the chemiluminescence method, and those that utilize infrared absorption (non-dispersive infrared absorption method).

The solution conductivity method requires a stirrer bar to be placed at the front stage to chemically treat interfering gases. Also, since the moisture in the gas has a large effect, it is cooled and dehumidified. Therefore, there is a loss of NH3 in these parts, which impairs the true value. Chemiluminescence method is N
Since only the single component O can be measured, the NH3 in the exhaust gas is converted to NO using a converter, the amount is measured as the total amount of NO, and the amount of NH3 is then measured by subtracting the amount of NO from that total. ing. In this kind of approach, N
There are problems with the non-dispersive infrared absorption method, such as whether 100% of the H3 gas is converted into the target component in a short period of time, and the conversion efficiency gradually decreasing.

Furthermore, since both methods are greatly affected by humidity, it is necessary to dehumidify them in the previous stage, and NH3 loss occurs, similar to the solution conductivity method. Further, there is a method technically similar to the present invention called a higher-order derivative method (higher-order differential method). This high-order derivative method optically measures the differential value of the spectrum by vibrating either the input loss slit or the exit slit of the spectrometer, and then scans the wavelength by rotating the spectrometer's diffraction grating over time. In this method, a differential spectrum (generally a second-order differential spectrum) is obtained by differentiating the absorption spectrum, and quantitative determination is made from the difference between the peaks and valleys of this differential spectrum.

If there are no impurities in the sample gas, measurement can be performed using the higher-order derivative method, but if the sample gas contains many impurities such as nitrogen monoxide and sulfur dioxide, such as flue gas, these impurity gases may be detected. The ammonia gas concentration cannot be measured correctly due to the influence of overlapping absorption vectors.

The present invention eliminates the drawbacks of the prior art and provides an accurate automatic continuous ammonia gas analyzer that directly measures the instantaneous value of the ammonia gas concentration contained in impure gas such as flue gas. This is an ammonia gas analyzer based on the self-modulating light absorption method, which is a variation of the dispersion ultraviolet absorption method that uses the ultraviolet absorption of sample gas, and is capable of measuring ultraviolet absorption of sample gas at high temperatures. This ammonia analyzer is characterized in that the light absorption cell is heated to a high temperature in order to achieve this, and that the interference of SO2, which is contained in a large amount in flue gas, is removed.

First, the self-modulation light absorption method, which is the measurement principle employed in the ammonia gas analyzer according to the present invention, will be explained.

As shown in FIG. 1, the absorption peak λ of the gas to be measured. When wavelength modulation of frequency ω is applied between both ends λ1 and λ2,
Due to the presence of the gas to be measured, a light intensity modulation signal with a frequency of 2ω is obtained. Since the amplitude of this light intensity modulation signal is proportional to the gas concentration, this method determines the gas concentration from this amplitude. In FIG. 1, the λ axis represents wavelength, the I axis represents transmitted light intensity, and the t axis represents time. In the figure, curve A is an absorption spectrum, ωt is a wavelength modulation signal, and 2ωt is a light intensity modulation signal. To actually perform this, that is, to apply wavelength modulation, as shown in FIG. 2, the exit slit of the spectrometer is vibrated back and forth in the direction of the arrow in the figure.

In FIG. 2, 120 is a spectrometer, 121 is an input loss slit, 122 is a collimator mirror, 123 is a collector mirror, 124 is a diffraction grating which is a wavelength dispersion element, 125 is an exit slit, 126 is a photomultiplier tube, 12r represents the optical axis within the spectrometer. When the exit slit 125 vibrates back and forth in the direction of the arrow A in the figure, the exit slit 1
The light flux passing through the exit slit 25 moves along the diagonally shaded area surrounded by the broken line A and the broken line opening along with the vibration of the exit slit opening 25. The luminous flux indicated by the broken line A corresponds to the wavelength λ1 in Fig. 1, and the luminous flux at the beginning of the broken line corresponds to the wavelength λ1.
2, wavelength modulation can be applied between the wavelength λ1 and the wavelength λ2. Wavelength modulation can be achieved by fixing the exit slit and vibrating the input loss slit, or by fixing both the input loss slit and the exit slit and installing a vibrating mirror inside the spectrometer to swing the optical axis inside the spectrometer. Wavelength modulation can be applied.

Therefore, the present invention does not limit the method of applying these wavelength modulations. Next, the ultraviolet absorption spectrum of ammonia gas at room temperature is as shown in FIG.

In the figure, λ on the horizontal axis represents wavelength in Nm, and a on the vertical axis represents absorption intensity. Single line A is the ultraviolet absorption spectrum of ammonia gas, and there is almost no absorption beyond 215 nm. There is strong absorption at wavelengths shorter than 200 nm, but if the absorption wavelength at wavelengths shorter than 200 nm is used as the measurement wavelength, there will be interference effects due to absorption of oxygen in the air and absorption of hydrocarbons, especially unsaturated hydrocarbons, and aromatic hydrocarbons. I don't like it when I receive it.

Therefore, absorption wavelengths longer than 200 nm must be used as measurement wavelengths; however, wavelengths longer than 200 nm are affected by interference due to absorption of nitrogen monoxide and sulfur dioxide gas, which are contained in large quantities in flue gas. That is, the absorption spectra of nitric oxide and sulfur dioxide gas are as shown in Figure 4.
It can be seen that there is absorption near 226 nm, and unless these absorptions are avoided, there will be an interfering effect on the ammonia analysis value. However, even if the measurement wavelength is set to a wavelength that avoids these absorptions of nitric oxide, the interference effect does not necessarily become zero.

Among the absorption wavelengths of ammonia gas, the wavelengths that do not overlap with the absorption of nitric oxide are 201 nm, 209 nm, and 213 nm.
, 217 nm, etc., but it was confirmed experimentally that 2
01 nm, 213 nm, and 217 nm have a large interference effect with nitric oxide, and are not preferred as measurement wavelengths. Fifth
The figure shows the magnitude (wavelength characteristics) of the self-modulated light absorption signal obtained for each component gas. From Figure 5, the wavelength where the interference effect of nitric oxide is small is around 210 nm (A in the figure).
) or around 220 nm (B in the figure). The authors first filed a patent application related to this matter in 1983.
4001, one of the features of the present invention is that point B (219 nm) near 220 nm is used as the measurement wavelength.

However, as shown in Fig. 6, this point B (219 nm) is the intermediate wavelength between 217 nm (λ, in the figure) and 221 nm (λ2 in the figure), which are the absorption peaks of ammonia gas.
This method takes advantage of the fact that the absorption spectrum of ammonia gas is periodic.

In FIG. 6, the horizontal axis λ indicates wavelength, and the vertical axis 1 indicates transmitted light intensity.

Curve A is the absorption spectrum of ammonia gas, and point P
1 is the absorption peak at wavelength λ1 (217 nm), P2
indicates an absorption peak at wavelength λ2 (221 nm).
Wavelength B is the same wavelength as wavelength B in FIG. In addition, the absorption at 217 nm and 221 nm is very weak in gases at room temperature. Therefore, if point B is the measurement wavelength at room temperature, the sensitivity of ammonia is very poor, and the sensitivity of ammonia is relatively low.
This is undesirable because the interfering influence of sulfur dioxide gas increases.

The experimental results shown in Figure 5 are for a gas temperature of 200°C,
As long as the measurement wavelength is 219 nm, it is clear from the experimental results shown in Figure 5 that gases at a high temperature of about 200°C must be measured, and this is an essential element of the present invention as well. It can be understood that the limitation of the measurement wavelength to 219 nm is also a major element of the present invention obtained from the experimental results. Furthermore, the shape of the absorption spectrum changes depending on the width of the input loss slit or the width of the exit slit of the spectrometer.

This is because when the slit width is widened, the resolution deteriorates and steep spectra are smoothed out. For this purpose, a spectrometer is generally used by narrowing the slit width to some extent to increase resolution, but in order to reduce the interference effect of sulfur dioxide gas, the following measures were taken in the present invention. In other words, since the absorption spectrum of sulfur dioxide gas has a periodicity of approximately 2 nm, the width of both slits is 2 nm in terms of wavelength.
The absorption spectrum of sulfur dioxide gas was made almost flat.
As shown in Figure 7, as long as the absorption spectrum is captured with a 2 nm wide slit, the light intensity will be λ
This makes good use of the fact that it does not change at all even if you move it in one direction. That is, in Fig. 7, the slit width S
is equal to the period T of the spectrum A, the slit has a wavelength λ
Even when moving in the direction, the total amount of light passing through the slit is 1 s (
The black area in the figure) is due to the fact that there is no change. The experimental results shown in FIG. 5 show that the slit width (wavelength conversion value) for both the entrance loss slit and the exit slit is 1.2 nm, and a slit width narrower than this is not preferable because the interference effect of sulfur dioxide gas becomes large. Furthermore, if the slit width is 2.0 nm or more, the sensitivity to ammonia will drop significantly, so the slit width is preferably 1.2 nm to 2.0 nm in terms of wavelength. When the slit width is selected in this way, the interference coefficient of the interference effect of sulfur dioxide gas on the ammonia measurement value is reduced to about 1/20. In other words, when the sulfur dioxide gas is below 1000 pores, the indicated value of ammonia will be affected by interference to the extent that it deviates from the true value by about 50 PP1. However, in coal-fired boilers, C heavy oil-fired boilers, etc., the sulfur dioxide gas concentration is as high as 600PF to 1000Pi1, as mentioned above, so the interfering influence of sulfur dioxide gas must be minimized.

Therefore, in the present invention, the interference influence is further reduced as follows.

That is, the absorption spectrum of sulfur dioxide gas has a periodicity of approximately 2 nm, while the absorption spectrum of ammonia gas has a periodicity of approximately 4 nm. As shown in Figure 8, when wavelength modulation is applied to a frequency ω with an amplitude of 4 nm in terms of wavelength, the frequency of the light intensity modulation signal generated by the absorption vector of sulfur dioxide gas becomes 4 ω. do. In other words, by applying modulation with an amplitude twice the periodic width of 2 nm of the absorption spectrum of sulfur dioxide gas, the self-modulation signal is set to 4ω instead of 2ω, making it possible to remove the 4ω signal by an electric circuit. It is possible. From the design of the bandpass filter, it seems that this amplitude is not limited to 4 nm and may be greater than 6 nm or 8 nm, but since the width of the absorption spectrum of ammonia gas is 4 nm, the amplitude should not be increased beyond this. makes no sense since it would also weaken the self-modulating signal of ammonia gas. Further, making the amplitude smaller than 2 nm of the spectral width of sulfur dioxide gas is also ineffective because the reduction in sensitivity of ammonia gas is significantly greater than the reduction in sensitivity of sulfur dioxide gas, and therefore the interference effect becomes large. In reality, the amplitude does not necessarily have to be twice the obvious width of 2 nm of the absorption spectrum of sulfur dioxide gas, and in the experiment shown in FIG. 5, the modulation amplitude is 3.4 nm. Even if the measurement wavelength of ammonia gas is the above-mentioned point B (219 nm), the slit width of the spectrometer is 1.2 nm, and the modulation amplitude is 3.4 nm,
The disturbing influence (interference) of sulfur dioxide gas cannot be completely eliminated. It should be noted that the interference does not increase proportionally to the concentration of sulfur dioxide gas, but rather increases by approximately 1000PF1 (17
) The sulfur dioxide concentration is only a whisper, and moreover, the interference value is a relatively flat function at a sulfur dioxide concentration of about 1,000 units. Figure 9 shows the interference of sulfur dioxide gas under the above conditions.

In FIG. 9, the horizontal axis N indicates the sulfur dioxide gas concentration, and the vertical axis indicates the output of the measuring device as the ammonia gas concentration.
That is, if sulfur dioxide gas is present in the gas to be measured, an output corresponding to the interference curve K in FIG. 9 will be generated. This interference is based on the principle of superposition. For example, when measuring a gas in which 25 ammonia gases and 400 ppm of sulfur dioxide gas are present at the same time,
The output 5PF (C in the figure) corresponding to the sulfur dioxide gas concentration 400PP01 (N2 in the figure) is superimposed, and the measuring instrument output is 30P.
It becomes I1. However, the interference curve in FIG. 9 depends on the center wavelength of the set wavelength modulation (wavelength B in FIG. 6), and the example in FIG. 9 was observed at 219.6 nm.

Also, this interference curve depends on the slit width and slit amplitude, but in any case, if expressed as an approximate formula, K=a(N-
b) It is a curve that can be expressed as 2+D.

The measurement value output 30PP1 mentioned above is the true value of ammonia (25
PF), it is necessary to make a correction for this amount.

This correction can be performed by calculating and removing the superimposed interference while simultaneously measuring the sulfur dioxide gas concentration. In addition, the concentration range of sulfur dioxide gas is 200PP1 (
If it fluctuates between 400 pIm (N1 in Figure 9) and 400 pIm (N2 in Figure 9), the interference amount will fluctuate (C in Figure 9).
and 7 o (D in Figure 9), and the range of variation is 2.
1) Since Pl is small, by always subtracting a constant value of 6 PIU as the ammonia output, ±1 PI1
Ammonia concentration can be measured with an accuracy of .

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 10 shows a first embodiment of an ammonia gas analyzer, which is an automatic continuous ammonia analyzer for flue gas.

The exhaust gas is collected by sampling probe 1 inserted into flue 1.
The light is sucked in by a suction pump 12, removed from dust by a dust removal filter 11, and continuously introduced into a light absorption cell 110.

A cell heater 113 is wound around this light absorption cell 110, and the gas temperature inside the light absorption cell 110 is set to about 20°C by PID control of a temperature control device 114, so that the absorption of ammonia gas is 217 nm. and 221nm
It is made to become stronger. On the other hand, the light emitted from the light source 101 is made into a parallel beam by the collimator lens 102, and then passes through the entrance window 111 of the light absorption cell to the light absorption cell 1.
10 and exits from the exit window 112.

The parallel light flux emitted from the exit window 112 is sent to the collector lens 1.
04, the light is focused on the input loss slit 121 of the spectrometer and enters the spectrometer 120, and the absorption spectrum of the ammonia gas is transmitted to the measurement exit slit 1 by the dispersion element 124.
The image is focused around 25.

The light passing through the measurement exit slit 125 reaches the light receiving surface of the photomultiplier tube 126. The exit slit 125 is cut in a slit plate 130, which is attached to the free end of one leg of the U-shaped tuning fork 135 and drives the tuning fork 135 sinusoidally at an angular frequency ω by a tuning fork drive 140. The outlet slit 125 is vibrated by causing natural vibration. By vibrating the exit slit 125 in this manner, the wavelength of the light passing through the exit slit 125 is modulated by the angular frequency ω. As mentioned above, the flue gas is continuously introduced into the light absorption cell 110. Therefore, if ammonia gas is mixed in the flue gas, the suction vector of ammonia gas will be generated near the exit slit 125. is imaged. Then, when the exit slit 125 is vibrated to apply wavelength modulation at the angular frequency ω as described above, the light reaching the light receiving surface of the photomultiplier tube 126 has an amplitude proportional to the ammonia gas concentration and an angular frequency 2ω.
A light intensity modulation signal of This is based on the principle of the self-modulated light absorption method described above (see FIG. 1U1).

Furthermore, when sulfur dioxide gas is present, the interference of its concentration is superimposed on the optical modulation signal. Measurement exit slit 125
The wavelength of the light passing through is point B (219 nm) under the conditions described above.
) vibrates around the center. Then, the signal processing device 200 converts the amplitude of this light intensity modulation signal into the tuning fork driving device 14.
Detects a signal component synchronized to a frequency twice that of 0. The output signal of the signal processing device 200 is a signal proportional to the ammonia concentration and an interference component of sulfur dioxide gas superimposed thereon. On the other hand, the sulfur dioxide gas concentration is determined by receiving the light that has passed through the sulfur dioxide gas measurement exit slit 125' (center wavelength 300 nm) with a photomultiplier tube 126', and photoelectrically converting the light intensity modulation signal with an amplitude proportional to the sulfur dioxide gas concentration. do.

A signal processing device 20' detects a signal component synchronized with twice the frequency of the tuning fork driving device 14' from the signal photoelectrically converted by the photomultiplier tube 126'. Sulfur dioxide gas is 300
There is also periodic absorption near nm, and 300 nm is one of the absorption peaks, so the output signal of the signal processing device 20' corresponds to the sulfur dioxide gas concentration. The output signal of the signal processing device 20 corresponding to this sulfur dioxide gas concentration is input to the function generator 300. This function generator 300 is a polygonal approximation of the interference curve K shown in FIG. 9, and is designed to generate an output signal V(n) for an input signal n. The output signal of this function generator 300 is input to a subtraction circuit 400. On the other hand, the output signal of the signal processing device 200 is input to this subtraction circuit. Then, in the subtraction circuit 400, the output signal of the function generator 300 (the interference amount of sulfur dioxide gas, that is, the ammonia gas concentration conversion output) is converted from the output signal of the signal processing device 200 (the ammonia output superimposed with the interference amount of sulfur dioxide gas). is subtracted. In this way, the output signal of the subtraction circuit 400 becomes an amount proportional only to the ammonia gas concentration. The output signal of the subtraction circuit 400, which is proportional only to this ammonia gas concentration, is input to the output display device 500 and displayed. The output display device 500 is a voltmeter or a voltage recorder, and has a scale corresponding to the ammonia gas concentration. The signal processing devices 200 and 20' are synchronous detection devices generally called lock-in amplifiers. Note that 100 indicates a detection section. Next, a second embodiment of the present invention is shown in FIG. 11, and will be described with reference to FIG. Ammonia gas in the exhaust gas in the flue 1 is detected by the detection unit 10' in the same manner as in the first embodiment.

At this time, the output signal of the signal processing device 200 has the interference of sulfur dioxide gas superimposed thereon, as described above. On the other hand, a T-shaped joint pipe 15 is provided in the middle of the conduit, and exhaust gas is simultaneously sucked into the sulfur dioxide gas analyzer 600 by a suction pump 12'. The output signal of this sulfur dioxide gas analyzer 600 is input to a function generator 300, and the output signal of this function generator 300 is input to a subtraction circuit 400. On the other hand, the output signal of the signal processing device 200 is input to this subtraction circuit. Then, the subtraction circuit 400 subtracts the output signal of the function generator 300 from the output signal of the signal processing device 200. Therefore, the output signal of the subtraction circuit 400 is proportional only to the ammonia gas concentration. The sulfur dioxide gas analyzer used in this example is an automatic measuring device that can measure instantaneous values.
It doesn't matter what type it is. For example, a self-modulation light absorption method, a non-dispersive infrared absorption method, or a solution conductivity method may be used. Detection unit 1 used in this example
0' is similar to the detection unit 100 of the first embodiment, but differs in that it does not have the function of simultaneously measuring sulfur dioxide gas.

That is, the detection unit 100 of the first embodiment includes the photomultiplier tube 13'', the tuning fork drive device 14'', and the exit slit 12''.
55, the signal processing device 20 'but the detection unit 10 of the second embodiment
``Then it's excluded. Here, the function generator used in the first and second embodiments will be explained. The sulfur dioxide gas measurement output 20' or 600 is converted by the AD converter 301 and input to the shift register 302.

(Here, the AD-converted output specifies the address of the p-ROM 3O3.) The signal temporarily held in the shift register 302 is input to the p-ROM 3O3. P-
An address in the P-ROM is designated by a signal input to the ROM, and its contents are output from the designated address. (
The sulfur dioxide gas interference curve shown in FIG. 9 is stored in advance in the P-ROM. ) Contents output from P-ROM (
(ammonia gas interference with sulfur dioxide gas) is temporarily held in a shift register 304 and input to a DA converter 305. The signal input to the DA converter is converted into an analog quantity by DA conversion. A timing circuit 306 takes timing between each circuit. This analog quantity is the ammonia interference output with respect to the sulfur dioxide gas concentration. Next, a third embodiment will be described with reference to FIG. 13.

The detection section 10'' used in this embodiment has the same configuration as the detection section 10'' used in the second embodiment. That is, the part that detects sulfur dioxide gas is removed. The output signal of the signal processing device 200 is an output proportional to the ammonia gas concentration and an interference component of sulfur dioxide gas superimposed thereon.

A subtraction circuit 400 subtracts a constant voltage from the output signal of the signal processing device 200. This constant voltage is generated by a function generator 300 or a reference voltage generation circuit consisting of a simple circuit, and is adjusted and set to a voltage between points C and D in FIG. The signal subtracted by the subtraction circuit 40 is proportional to the ammonia gas concentration with an error of ±1 PIX1 as long as the sulfur dioxide gas concentration fluctuates between N and N2 in Fig. Interference can be removed.

The concentration of sulfur dioxide gas in the exhaust gas from heavy oil-fired boilers and coal-fired boilers used in Japan is 200PyI1.
˜400PF1, so this third embodiment is also effective in measurements within the above error range.

The spectroscope 120 used in the example has a focal length of 250 m2.
The number of lines of the 11 diffraction grating is 1200 lines/1L1L,
The inverse dispersion is 2.6 nm/1t1L. The width of the input loss slit and the exit slit was 0.5 ml, and the converted wavelength value was 1.3 nm. In general, the slit width of a spectrometer is 0.5 nm to 1 nm, since the wider the resolution, the worse the resolution.
．． 0 nm, but as mentioned above, 1.3 nm was adopted in order to reduce the interfering influence of sulfur dioxide gas. Also,
The wavelength tuning of the spectrometer determines the performance of this analyzer.

In other words, as mentioned before, the exit slit is at wavelength 2.
The location of the exit slit 125 must be adjusted to pass 19 nm light. In this example, this adjustment was performed as follows. The spectrometer 120 has an input loss slit 121 according to the optical drawing designed in advance.
, a collimator mirror 122, and a diffraction grating 124 which is a dispersive element.
and a collector mirror 123. Then, the optical axis runs through the spectrometer as designed, but at this time, the wavelength is 219 nm.
and the optical axis of the 253.7 nm emission line of mercury are determined in advance. This optical diagram is shown in FIG. Of course, the imaging positions of 219 nm and 253.7 nm are determined at the time of design.

A slit plate 130 was prepared in which two slits were carved at intervals equal to the distance between these images. One of these slits is the exit slit 125 for measuring ammonia, and the other slit is the exit slit 125 for measuring the mercury.
This is an adjustment slit 128 that passes 53.7 nm. When adjusting the analyzer, the light beam from the mercury lamp is input through the input loss slit 121 of the spectrometer, and the mercury bright line 2
The tuning fork 135 was mounted so that the slit plate 130 was placed at a position where the 53.7 nm light was emitted from the adjustment slit. In reality, this tuning fork 135 was placed on a fine movement table, and the slit position was adjusted by moving the tuning fork using this fine movement table. A general spectrometer has a mechanism for rotating the dispersive element 124 for wavelength scanning, but in this embodiment, the dispersive element 124
was fixed and installed as designed. Further, the vibration amplitude of the exit slit in this example was adjusted to 1.3 mm. This amplitude is 3.3 nm in terms of wavelength. As explained above,
According to the present invention, since the light absorption cell is heated to a high temperature to utilize the light absorption of the gas in a high temperature state,
Ammonia gas has an absorption peak at the long wavelength end (217 nm), which has very weak absorption at room temperature, and an absorption peak (221 nm) at the long wavelength end, which has very weak absorption at room temperature.
The measurement wavelength was able to be an intermediate wavelength (219 nm) between the two wavelengths.

To this end, we provide an ammonia analyzer that can avoid absorption of oxygen, unsaturated hydrocarbons, aromatic hydrocarbons, nitrogen monoxide, etc. that have absorption in the ultraviolet region, and has very small interference effects from these interfering substances. be able to. Furthermore, the interference of sulfur dioxide gas is reduced by widening the width of the inlet or exit slit and increasing the vibration amplitude of the exit slit, with the aim of skillfully utilizing the fine features of the spectral structures of sulfur dioxide gas and ammonia gas. This makes it possible to remove the interference of sulfur dioxide gas and provide an ammonia analyzer for flue gas using a spectroscopic analysis method, which was previously impossible to achieve. Currently, dirty exhaust gas (
Since there is no other automatic measuring device that measures ammonia concentration in exhaust gas (exhaust gas with high concentrations of nitrogen oxides and sulfur dioxide), the present invention has great effects on industry and environmental conservation.

[Brief explanation of the drawing]

FIGS. 1 and 2 are diagrams explaining the principle of self-modulating light absorption method. FIG. 3 is a diagram showing the absorption spectrum of ammonia gas in the ultraviolet region. FIG. 4 is a diagram showing the absorption spectra of nitric oxide (A in the figure) and sulfur dioxide gas (B in the figure) in the ultraviolet region. FIG. 5 is a diagram showing the wavelength characteristics of a self-modulated optical absorption signal experimentally obtained by the inventor,
It is a figure showing the characteristics of ammonia gas, nitrogen monoxide, and sulfur dioxide gas. FIG. 6 is a diagram for explaining the relationship between the measurement wavelength and the absorption spectrum of ammonia gas in the present invention, and is a diagram for explaining the principle of the present invention. Figures 7 and 8
The figure is an explanatory diagram of the principle of the present invention using a self-modulated light absorption method. FIG. 9 is a diagram showing the interfering influence of sulfur dioxide gas in the present invention. FIG. 10 is a diagram showing a first embodiment of the present invention. FIG. 11 and FIG. 13 are diagrams showing a second embodiment and a third embodiment of the present invention. FIG. 12 is a block diagram showing the function generator. FIG. 14 shows the second and third embodiments of the present invention.
FIG. 2 is an optical diagram inside a spectrometer used in an example. 1: flue, 1
1: Dust removal filter, 12: Suction pump, 100: Detection unit, 101: Light source, 110: Light absorption cell, 113: Cell heater, 114: Temperature control device, 120: Spectrometer, 1
21 two-person loss slit, 124: dispersion element (diffraction grating in this example), 125: exit slit, 126: photoelectric conversion element (photomultiplier tube in this example), 140: slit driving device, 200: signal processing device , 300: function generator, 400. Subtraction circuit, 500: Output display device, 600:
Sulfur dioxide gas analyzer.

Claims (1)

[Scope of Claims] 1. A light source 101 that emits ultraviolet rays, means 110 for passing a light beam from the light source into a medium to be measured containing ammonia gas and sulfur dioxide gas maintained at a substantially constant high temperature, and In the first or second stage,
Means 1 for wavelength modulating the light beam into a sinusoidal waveform with an angular frequency ω
35, a device 100' for obtaining a light intensity modulation signal with an angular frequency of 2ω brought about by the absorption characteristics of sulfur dioxide gas and ammonia gas with wavelengths in the range of 217 nm to 221 nm; a signal processing device 200 that generates a signal in which an output corresponding to the ammonia gas concentration is added to an interference output converted to the ammonia gas concentration due to the sulfur dioxide gas; a sulfur dioxide gas measurement that measures the sulfur dioxide gas concentration contained in the medium to be measured; Means 200', 600
and; a function generator 300 that generates an ammonia gas concentration conversion output that is specific to the wavelength range and corresponds to the sulfur dioxide gas concentration measured by the sulfur dioxide gas measuring means; and; an ammonia gas analyzer comprising: means 400 for outputting the true concentration of ammonia gas in the medium to be measured by subtracting the output of the analyzer; a vibration device 135 for vibrating either the entrance slit, the exit slit of the spectrometer, or a vibrating mirror provided in the spectrometer; a photoelectric converter 126 that receives the light beam, and the slit width of the entrance slit or the exit slit is 1.2 nm to 2 nm in terms of wavelength.
and the amplitude of the vibration is 2 nm to 4 in terms of wavelength.
An ammonia gas analyzer characterized in that it is a nm. 2. The function generator generates an ammonia gas concentration conversion output K corresponding to the sulfur dioxide gas concentration N, and makes the input/output relationship satisfy the following formula within a predetermined error range. An ammonia gas analyzer according to claim 1, characterized in that: Formula: K=a(N-b)^2+D However, -0.5<a≦0, b>0, D>0