JPH1010040A - Gas cell for gas analyzer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas cell whose detecting sensitivity is not influenced by a flow rate and flow speed of gas by devising the constitution of the gas cell in a gas analyzer. SOLUTION: A gas cell of a gas analyzer is provided with a passage 10 which introduces a gas component and the infrared light to be measured and derived the gas component and the infrared light after the infrared light is absorbed by the gas component. This passage 10 is provided with an outer wall 10a having a conical wall part 13 and an inner wall 10b having a conical wall part 11 arranged in the axial direction so as to be opposed to this. The infrared light is introduced to the passage 10 from an infrared light introducing port 17 so as to advance by being multiply reflected in a spiral shape to the periphery of its axis between both wall parts 11 and 13. Gas is also introduced to the passage 10 from a gas introducing port 15 so as to advance in its axial direction along a part between both wall parts 11 and 13.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas analyzer for analyzing components in a gas, such as a Fourier transform infrared spectrophotometer (hereinafter referred to as "FTIR") gas analyzer, and more particularly, to a gas analyzer.
The present invention relates to a gas cell suitable for use in the gas analyzer.

[0002]

2. Description of the Related Art In recent years, studies on reduction of air pollutants in exhaust gas of an internal combustion engine have been actively conducted from the viewpoint of air pollution prevention. Here, since air pollutants are emitted as various types of gas components, these gas components
It can be detected by an FTIR gas analyzer.

An FTIR gas analyzer uses a Michelson interferometer or the like to measure the infrared absorption spectrum of a gas component by interference spectroscopy and analyze the component concentration. In the measurement of gas components, an infrared absorption spectrum obtained by introducing an analysis gas into a gas cell and irradiating infrared light is detected by a detector. In order to obtain sufficient sensitivity for detecting an infrared absorption spectrum, it is necessary to make multiple reflections of infrared light in a gas cell, and usually a sufficiently long optical path length is formed. On the other hand, as means for obtaining a long optical path length in the gas cell, (1) a configuration in which a plurality of mirrors are placed in a gas cell having a large volume and the incident infrared light is reflected multiplely by the mirror; There is a configuration in which the inner peripheral surface of a pipe-shaped gas cell is coated with gold, and the gold is used to multiple-reflect infrared light (see Japanese Patent Application Laid-Open No. 4-1557).

[0004]

However, in the former case, since the capacity of the gas cell is large, the gas replacement speed in the gas cell is reduced, and the response time of the gas component detection is delayed. Here, in order to increase the response time of gas component detection while keeping the replacement speed low, it is necessary to increase the flow rate of the analysis gas or increase the capacity of the suction pump of the gas sampling device. For this reason, there is a problem that the detection sensitivity is easily affected by the flow rate and the flow velocity.

On the other hand, in the latter case, the length of the optical path is increased in order to obtain the detection sensitivity properly. As a result, the flow path of the gas cell becomes too long, and the pressure loss of the measurement gas in the pipe increases. There is. To cope with the above, the detection sensitivity is improved by increasing the number of multiple reflections, the pressure loss is reduced by shortening the gas flow path, and the gas replacement speed is reduced by reducing the flow path. It is desired to realize a gas cell in which the detection sensitivity is not affected by the flow rate and the flow velocity by achieving the three conditions of improving the pressure.

Therefore, the present invention provides a gas analyzer in which the detection sensitivity is not affected by the gas flow rate and gas flow rate by devising the configuration of the gas cell in the gas analyzer based on the above viewpoint. Aim.

[0007]

According to the first to fourth aspects of the present invention, a flow path of a gas cell provided in a gas analyzer has a conical outer wall portion, A conical inner wall along the inner peripheral surface of the portion and spaced axially therefrom. Also, for the flow path,
The infrared light is introduced so as to be spirally multi-reflected around the axis between the outer wall and the inner wall so as to travel therethrough. And is introduced so as to advance in the axial direction.

For this reason, the gas traveling in the axial direction of the flow path absorbs infrared light which is helically reflected multiple times between the conical outer wall and inner wall facing each other. In this case, as described above, the inner wall portion and the outer wall portion facing each other are both formed in a conical shape, and the traveling direction of the gas proceeds along the axial direction of the flow path. It is significantly shortened. Therefore, the pressure loss in the gas flow path can be significantly reduced.

Further, as described above, the inner wall portion and the outer wall portion facing each other are both formed in a conical shape, and the infrared light travels in a helical manner while multiple-reflecting the infrared light. The optical path length of the infrared light can be increased while reducing the volume between the parts, that is, the capacity. Therefore, the gas replacement speed can be increased by reducing the capacity, and the detection sensitivity as a gas cell can be increased by increasing the optical path length of the infrared light. This means that the detection sensitivity of the gas cell can be prevented from being influenced by the flow rate and the flow velocity of the gas, while ensuring the miniaturization of the gas cell.

Here, as in the invention according to claim 3,
Each introduction position of the infrared light and the gas with respect to the flow path,
When both are located at one axial end of the outer wall portion,
Alternatively, as in the invention according to claim 4, the introduction position of the infrared light with respect to the flow path is located at one axial end of the outer wall, and the introduction position of the gas with respect to the flow path is defined by the outer wall. Claim 1 even when positioned at the other end in the axial direction.
Alternatively, the same function and effect as the invention described in 2 can be achieved.

[0011]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic configuration of a gas analyzer to which the present invention is applied, and the gas analyzer has a gas cell S constituting a main part of the present invention.
The gas cell S has a flow path 10, and the flow path 10
Is composed of an inner wall 10a and an outer wall 10b that houses the inner wall 10a. As shown in FIG. 1, the inner wall 10a is integrally formed by a conical plate-shaped wall portion 11 and a disc-shaped wall portion 12. On the other hand, the outer wall 10b
The conical plate-shaped wall portion 13 and the U-shaped cross-section wall portion 14 are integrally formed.

Thus, the inner wall 10a is formed in the conical plate-like wall portion 1.
At 1, the disc-shaped wall 12 is supported by the rod 12a at the center of the U-shaped cross-section wall 14 of the outer wall 10b so as to be concentric with the conical plate-shaped wall 13 of the outer wall 10b. ing. Here, between the inner wall 10a and the outer wall 10b,
A space is provided between the inner wall 10a and the outer wall 10a.
In b, on each of the opposing surfaces of the conical plate-shaped wall portion 11 and the conical plate-shaped wall portion 13, each of the reflection films 11a and 13a is formed by coating by gold vapor deposition or the like.

The flow path 10 has a gas inlet 15 for introducing a gas for analysis and a gas outlet 16 for introducing the gas.
As shown in FIG. 1, the gas inlet 15 is formed so as to face the tip of the conical plate-shaped wall portion 11 of the inner wall 10a. On the other hand, the gas outlet 16 is connected to the outer wall 1.
0b is formed at the lower part of the U-shaped cross-section wall portion 14. The flow path 10 has an infrared light inlet 17 for introducing infrared light from the light source L and an infrared light deriving window 1 for extracting the introduced infrared light.
The infrared light inlet 17 is formed near the gas inlet 15 of the conical wall 13 of the outer wall 10b.

The infrared light introduction port 17 has an introduction window 17a formed therein.
The infrared light from the light source L is introduced into the flow channel 10 through the introduction window 17a. The infrared light from the light source L is 2 to 50 μm.
m. The infrared light is frequency-modulated by an interferometer (not shown) and then introduced into the flow path 10 through the infrared light introduction port 17. The introduction window 17a is made of an infrared light transmitting material such as ZnS or ZnSe.

On the other hand, the infrared light lead-out window 18 is formed on the upper part of the U-shaped wall portion 14 of the outer wall 10b, and the infrared light lead-out window 18 converts the infrared light introduced into the flow path 10 into a concave mirror. Derived toward 20. The infrared light exit window 18 is formed of the same material as the introduction window 17a. Concave mirror 2
0 indicates that the infrared light emitted from the flow path 10 is condensed and the detector 30
Reflects toward. The detector 30 is made of a semiconductor (for example, HgCdTe). The detector 30 detects the intensity of infrared light according to the wavelength and outputs the detected infrared light as an infrared absorption spectrum. Based on the infrared absorption spectrum, a specific component concentration in the analysis gas is calculated by a computer (not shown) using Lambert-Beer's law.

Incidentally, in the present embodiment, the shape and dimensions of the gas cell configured as described above are set as shown in FIG. 2 and FIG. 8. Axial length of inner wall 10a (conical plate-shaped wall 11) ... 19.2cm Distance from center of axis of inner wall 10a to disc-shaped wall 12 ... 9.6cm Radius of disc-shaped wall 12 of inner wall 10a ... 6 cm Axial length of outer wall 10b 20cm Maximum radius of conical plate-shaped wall 13 of outer wall 10b 10cm Also, the incident angle of infrared light with respect to the axis of infrared light inlet 17 is determined by the longitudinal section of gas cell S (see FIG. 2). ), The inner wall 10
is set to an angle α (α = 78 °) with respect to the inner wall 10a in the transverse section (see FIG. 3) of the gas cell S (indicated by a symbol H in FIG. 3).
(Β = 10 °). As a result, the infrared light travels spirally toward the infrared light outlet 18 along the two reflective films 11a and 13a while being multiply reflected between them.

Since the shape and size of the gas cell are set as described above, the capacity formed between the inner wall 10a and the outer wall 10b of the flow channel 10 is about 200 cc, and the two reflective films 11a
The optical path length of the infrared light traveling helically due to multiple reflection between and 13a was about 2.2 m. In addition, not limited to this,
The incident angle of the infrared light may be changed and set as necessary. In short, the infrared light introduced into the flow channel 10 from the infrared light introduction port 17 is formed between the two reflection films 11a and 13a. The infrared light outlet 18 spirals along these while being multiply reflected between them.
What is necessary is just to set so that it may progress toward a side. However, 0 ° <α
<90 ° and 0 ° <β <90 °, α
As β and β become larger, the number of times of multiple reflection of the infrared light traveling spirally increases.

In the present embodiment configured as described above, the analysis gas is introduced into the flow channel 10 from the gas inlet 15 as shown by the dashed arrow in FIG. It is assumed that the infrared light is introduced into the flow channel 10 from the infrared light inlet 17 as shown by the solid line arrow in FIG. Here, the infrared light inlet 1 for infrared light
Since the incident angle with respect to 7 is set as described above,
The infrared light is transmitted from the vicinity of the gas inlet 15 to both the reflection films 11a and 1a.
3a and spirally travels toward the infrared light outlet 18 side while being multiply reflected. On the other hand, the gas travels in the axial direction from the gas inlet 15 through the space between the two reflective films 11a and 13a.

Therefore, the infrared light that travels in a spiral shape while undergoing multiple reflections by the gas that travels as described above is absorbed at a specific wavelength according to the gas composition. In this case, the traveling direction of the gas is, as described above, the wall portion 11 of the inner wall 10a opposed to each other.
And the wall portion 13 of the outer wall 10b is formed in a conical shape, and travels along the axial direction of the flow path 10 unlike the spiral progression of the infrared light. Is significantly reduced. Therefore, the pressure loss in the gas flow path can be significantly reduced.

Also, as described above, the inner walls 1 facing each other
The wall portion 11a of the inner wall 10a and the wall portion 13 of the outer wall 10b are both formed in a conical shape, and the helical light travels while reflecting the infrared light in a multiple manner. The volume between the parts 13, ie the volume
The optical path length of the infrared light can be increased to about 2.2 m while being reduced to cc.

Therefore, the gas replacement speed can be increased by reducing the capacity, and the detection sensitivity as a gas cell can be increased by increasing the optical path length of the infrared light. This means that the detection sensitivity of the gas cell can be prevented from being influenced by the flow rate and the flow velocity of the gas, while ensuring the miniaturization of the gas cell. Therefore, there is also an advantage that a means for increasing the flow rate such as a gas sampling device is not required. When the gas replacement speed was measured by the gas cell of the present embodiment, the replacement speed was greatly reduced to about 1.5 seconds. Also, almost no pressure loss was measured.

In practicing the present invention, the light source L
Although the wavelength of the infrared light is set to 2 to 50 μm, the wavelength is not limited thereto, and the wavelength region of the infrared light may be set arbitrarily. In this case, a detector corresponding to this wavelength region is used as the detector 30.
It may be adopted as. In order to cut unnecessary wavelength regions, an optical filter may be used. The light is not limited to infrared light, but may be any light that is absorbed according to the gas composition.

In practicing the present invention, as shown in FIG. 3, the gas outlet 16 of the outer wall 10b of the flow path 10 is used.
An infrared light inlet 17 is formed in the vicinity (corresponding to the large-diameter side portion of the outer wall 10b), and the gas inlet path 1 communicating with the gas inlet 15 is formed.
9 may be modified so as to form the infrared light outlet window 18 at the peripheral wall opening (facing the gas inlet 15).

Here, the analysis gas is introduced into the flow path 10 from the gas introduction port 15 through the gas introduction path 19 as indicated by the arrow indicated by the broken line in FIG. It is assumed that light is introduced into the flow channel 10 from the infrared light introduction port 17 as shown by the solid line arrow in FIG. The angle of incidence of the infrared light is such that the infrared light introduced into the flow path 10 from the infrared light
The multi-reflection between a and 13a is set so as to spirally advance toward the gas inlet 15 along these.

Thus, the infrared light is spirally reflected toward the gas inlet 15 along the multiple reflection films 11a and 13a while being multiply reflected between the two reflection films 11a and 13a from the large diameter side of the flow path 10. On the other hand, the gas is supplied from the gas inlet 15 to the two reflective films 11a.
And 13a in the axial direction. Therefore, the infrared light traveling spirally while undergoing multiple reflections by the gas traveling in this way is absorbed at a specific wavelength, and the gas is absorbed by the gas outlet 16.
The infrared light exits from the infrared light exit window 18. Thereby, the same operation and effect as the above embodiment can be achieved.

In practicing the present invention, if both conical wall portions 11 and 13 are formed in a divergent shape, the same as in the above-described embodiment, even if the respective intermediate portions are both curved. The effect of the invention can be achieved.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing one embodiment of the present invention.

2 (a) and 2 (b) are a schematic longitudinal sectional view showing the shape and dimensions of the gas cell of FIG. 1 and an enlarged transverse sectional view passing through an infrared light inlet, respectively.

FIG. 3 is a schematic cross-sectional view showing a modification of the above embodiment.

[Explanation of symbols]

L: light source, S: gas cell, 10: flow path, 10a: inner wall,
10b: outer wall, 11, 13 ... conical wall portion, 11a, 13
a: reflective film, 15: gas inlet, 16: gas outlet, 1
7 ... Infrared light inlet, 18 ... Infrared light outlet.

Claims (4)

[Claims] 1. A gas cell comprising a flow path (10) provided in a gas analyzer for introducing an analysis gas and infrared light and extracting the gas and infrared light, wherein the flow path has a conical shape. An outer wall portion (13), and a conical inner wall portion (11) disposed along the inner peripheral surface of the outer wall portion and spaced in the axial direction, and the infrared light is transmitted by the outer wall portion. And the inner wall portion is introduced into the flow path so as to be spirally multi-reflected around the axis thereof and travels, and the gas flows along the outer wall portion and the inner wall portion. A gas cell for a gas analyzer, wherein the gas cell is introduced into the flow path so as to proceed in the axial direction. 2. The gas cell for a gas analyzer according to claim 1, wherein a reflection film (13a, 11a) is formed on each of the opposing surfaces of the outer wall portion and the inner wall portion that face each other. 3. The gas according to claim 1, wherein each of the introduction positions of the infrared light and the gas with respect to the flow path is located at one axial end of the outer wall. Gas cell for analyzer. 4. An introduction position of the infrared light with respect to the flow path is located at one axial end of the outer wall, and an introduction position of the gas with respect to the flow path is located at the other axial end of the outer wall. The gas cell for a gas analyzer according to claim 1, wherein the gas cell is located at: