JPS6038655B2 - gas analyzer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a gas dehumidification system in a gas analyzer.

Depending on the gas analyzer, the moisture content in the gas may appear as an error in the analytical concentration indication value.

For example, an infrared absorption analyzer utilizes the fact that molecules with a dipole moment absorb infrared rays at a wavelength unique to each molecule, creating a transition between vibrational energy levels. A device that enables concentration measurement by introducing a sample gas into a sample cell and measuring the attenuation rate of the infrared rays transmitted through the sample cell at wavelengths that are absorbed by the molecules whose concentration in the sample gas is to be measured. It is. However, if water is contained in the sample gas, water has the property of absorbing infrared rays over a relatively wide range of wavelengths, so the infrared wavelength absorbed by the molecule whose concentration in the sample gas is to be measured and the absorption by the water are different. In this case, even if the attenuation rate of the infrared rays at that wavelength is measured, a measured concentration value containing an error corresponding to the amount absorbed by moisture will be obtained. Therefore, it is desirable to remove as much moisture as possible from the sample gas. However, in general infrared gas analyzers, in order to increase the stability of operation, a reference cell is installed separately from the sample cell, which is filled with a gas that does not absorb infrared rays (such as nitrogen) as a reference gas.
A method is being explored to measure the difference in transmitted light between both reference cells. Therefore, in this method, if the water content in both the sample gas and the reference gas is made equal, errors due to water content cancel each other out, so no error occurs in the concentration measurement value.
To explain a specific example, infrared ammonia gas (NH3
) In the case of an analyzer, N in the sample gas is converted to nitrogen monoxide (NO) using a thermal converter, and the sum of the NO originally present in the sample gas and the converted NO is calculated as the first The sample gas containing the N ratio is passed through an infrared absorption cell, and the sample gas still containing the N ratio is passed through a second same cell, and the NH3 concentration in the sample gas can be determined from the difference in the amount of infrared absorption by both cells. In this case, if the moisture content of each gas passed through the first cell and the second cell is made equal, the measured NH
3 Concentration does not include errors due to moisture. There is only one infrared absorption cell, and the sample gas and reference gas are alternately switched over time to measure and store the amount of transmitted light at each time, and two temporally adjacent measurement values are constantly compared. The situation is the same in a type of gas analyzer that detects a difference, and measurement errors due to moisture can be eliminated by making the moisture contents of both the sample gas and the reference gas equal.

Gas dehumidifiers are used in connection with gas analyzers in this manner, and such dehumidifiers include those using electronic gas coolers of cooling dehumidification type and semipermeable membrane vapor phase dehumidifiers that do not. There is.

In the former case, the temperature of the gas at the outlet of the dehumidifier is 1 to 3.
It is controlled at ℃, and it is not possible to lower the butterfly point temperature any further because it will freeze. On the other hand, the latter semipermeable membrane vapor phase dehumidifier can relatively easily dehumidify up to a fog point temperature of 120 oo. If the degree of dehumidification is low and the sample gas contains a large amount of moisture, the optical system of analytical instruments such as infrared analyzers that have an optical system will become more contaminated, causing zero point drift in the indicator, and chemical In the case of a luminescent analyzer, span drift occurs in a similar manner, which prevents accurate analysis value indication. Therefore, semi-permeable membrane vapor phase dehumidifiers with high dehumidification capacity are superior to electronic gas coolers with poor dehumidification capacity. FIG. 1 is a sectional view of such a semipermeable membrane vapor phase dehumidifier, and FIG.
FIG. 3 is a cross-sectional view taken along -X'. See these figures. The semipermeable membrane vapor phase dehumidifier includes an outer tube 1, a number of inner tubes 3 supported inside the outer tube 1 via partition plates 2,
3, 3, and each inner tube 3 is made of a compound called NAFION, a product of E.I. DuPont, and has the function of selectively permeating water vapor from the inside to the outside through the tube. have.
Now, while introducing a wet sample gas containing water vapor into each inner tube 3 from the inlet and discharging it from the outlet 5,
When the dry gas for purging is passed through the outside of the inner tube 3 from the other inlet 6 toward the outlet 7, water vapor in the wet sample gas passes through the wall of the inner tube 3 and is purged to the outside. The semipermeable membrane gas phase dehumidifier has the above-described configuration and functions, and is used in gas analyzers for the reasons described above.

Now, FIG. 2 is a schematic diagram of a conventional method using a semipermeable membrane vapor phase dehumidifier in a gas analyzer.

Refer to the same figure. Sample gas collected by sampling probe 8 (assuming exhaust gas from a car, etc.)
is divided into two channels. First, the sample gas is first converted into N○ (nitrogen monoxide) in the NH3 (ammonia gas) converter 9, and then in the N02 (nitrogen dioxide) converter 10, the N02 in the sample gas is converted into N○ (nitrogen monoxide). are all converted to NO. The sample gas, which no longer contains NH3 and N02 in this way, is dehumidified by passing through the semipermeable membrane vapor phase dehumidifier 12 as a reference gas, and is sucked by the pump 13 and exits from the inlet a of the switching portion 14. Infrared gas analyzer 1 via b
After passing through the cell 15A of No. 5, it is dissipated into the atmosphere. In addition, as a second flow of the sample gas sampled by the probe 8, the sample gas first converts NQ in the sample gas into NO in the N02 converter 11. Therefore, NH3 and N
The sample gas containing O is dehumidified in the semi-permeable gas-phase dehumidifier 12a, then sucked into the pump 13a, and is emitted into the atmosphere through the inlet d and outlet c of the switching valve 14. In the infrared gas analyzer 15, the cell 15A is irradiated with infrared wavelength light from the light source 15B, and the amount of transmitted light is measured by the detector 15C. The measured value is sent to the holding/difference calculator 150 and held. In this way, first, the measured value for the reference gas is held in the holding difference calculator 15D. Next, the gas flow path is switched at the switching valve 14, and the reference gas that does not contain NH3 is sucked by the pump 13, and the switching valve 14
The sample gas containing NH3 is diffused into the atmosphere from the inlet a of the switching valve 14 through the outlet c, and is sucked by the pump 13a, and then passed through the inlet d and outlet b of the switching valve 14 to the cell 1 of the gas analyzer 15.
Let the 5A guide you. Then, if you carry out measurements in the same way as before, the measured values for the sample gas will be retained and
It is held in the difference calculator 150. Since the constant values on both sides are now available, the difference calculation unit 15D performs a difference calculation to determine the difference between the constant values on both sides, and the NH8 concentration can be determined from the result. By periodically switching the switching valve 14 using an appropriate means, the gas analyzer 15 can continuously
Concentration can be measured. Semipermeable membrane vapor phase dehumidifier 12,
Clean dry air (referred to as bag air) prepared separately was used as the purge dry gas used in the purge air 12a, and this air was sucked by the pump 16 and was suitable for the outside of the inner tube of the dehumidifier 12, 12a. .

However, these semipermeable membrane gas phase dehumidifiers have the disadvantage that the fog point temperature of the gas at the outlet changes depending on the ambient temperature, gas flow rate, pressure difference between the wet sample gas and the dry gas for purging, etc. In order to solve this problem, it has conventionally been necessary to take measures such as placing the dehumidifier itself in a tooth temperature bath to maintain a constant pressure, which has the disadvantage of increasing costs. This invention has been made in order to eliminate the drawbacks of the prior art as described above, and therefore, an object of the present invention is to improve the flow rate of each gas at the outlets of both dehumidifiers without using an expensive oak heating tank. An object of the present invention is to provide a gas analyzer of the type described above, in which the point temperatures are made the same, thereby making the moisture content in each gas the same, and preventing measurement errors caused by the moisture content from occurring. be. The main point of the configuration of the present invention is that in the conventional gas analyzer as described above, the sample gas discharged from the outlet of one of the two semipermeable membrane vapor phase dehumidifiers is dried for purging the other dehumidifier. The purpose is to use each gas as a gas, and to equalize the temperature of each gas at the outlet of both dehumidifiers.

Next, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 3 is a schematic configuration diagram showing an embodiment of the present invention.
When this figure is compared with FIG. 2 showing the conventional configuration, the differences are as follows. That is, it is dehumidified by the semi-permeable dark air phase dehumidifier 12, sucked by the pump 13, and
The gas enters the cell 15A of the infrared gas analyzer 15 through the inlet a and outlet b of the infrared gas analyzer 15, and the gas that exits the cell is not dissipated into the atmosphere as it is, but is further passed through the atmosphere diffusion pipe 17 and then into the second switching valve 18. The dry gas is supplied as a purge dry gas from the inlet a to the semipermeable membrane vapor phase dehumidifier 12a on the opposite side via the outlet b. Similarly, the semipermeable membrane vapor phase dehumidifier 12
The gas that is dehumidified by the pump 13a, sucked by the pump 13a, and exits the inlet d and outlet c of the switching valve 14 is further transferred to the semipermeable membrane gas phase on the opposite side from the inlet d to the outlet C in the second switching valve 18. It is supplied to the dehumidifier 12 as a purge dry gas. When the gas flow path is switched in the switching valve 14 and the gas dehumidified by the dehumidifier 12 is released through the inlet a and the outlet c in the switching valve 14, the second switching valve 1
If the gas flow pattern is also switched in synchronization with the first switching valve 14, the gas passes through the inlet d and outlet b of the switching valve 18, and then goes to the dehumidifier 12a on the opposite side for purge drying. Supplied as a gas. The gas dehumidified by the dehumidifier 12a is similarly supplied to the dehumidifier 12 on the opposite side as a purge dry gas. Other than the points mentioned above, the configurations of FIG. 3 and FIG. 2 are the same. Now, the pressure of the sample gas introduced into the inner tube of the dehumidifier 12 (or 12a) is negative pressure because it is sucked by the pump 13 (or 13a), but the purge gas is passed through the outside of the inner tube of the dehumidifier. Since the gas is sucked in by the pump 16 to have a more negative pressure than the wet sample gas, the partial pressure of water vapor in the wet sample gas is higher than that of the purge dry gas.

Therefore, the wet sample gas is dehumidified in the dehumidifier 12 or 12a. In a semipermeable membrane vapor phase dehumidifier, the dew point temperature of the gas at its outlet varies depending on the dew point temperature of the purge drying gas. There is also some variation depending on the product. According to the embodiment of this invention, the first
When the dehumidifying capacity of the dehumidifier is high (the output gas point is low), the dehumidified gas is supplied to the second dehumidifier on the other side as dry gas for purge. 2
The dehumidification capacity of the dehumidifier is increased (the dew point is lowered). On the other hand, since the gas with a higher fog point from the second dehumidifier is used as a purge dry gas for the first dehumidifier, which has a high dehumidifying capacity, the dehumidifying capacity of the first dehumidifier decreases. In this way, the dehumidifying capacities of the first and second dehumidifiers are eventually equalized, and the fog point temperatures of the respective gases dehumidified by both dehumidifiers do not approach the same value. Next, referring to FIG. 3, the reason why the gas exiting the infrared gas analyzer 15 is passed through the atmosphere opening tube 17 will be explained.

FIG. 4 is a cross-sectional view of the atmosphere-opening pipe.

Refer to the same figure. The atmosphere opening pipe 17 literally opens one end 17A to the atmosphere. Gas is exhausted from the cell 15A to the inlet 17B farthest from the open end 17A. Gas is then sent toward the switching valve 18 from the outlet 17C. By using such an atmosphere opening pipe 17, the pressure inside the cell 15A of the gas analyzer 15 can be maintained at approximately atmospheric pressure. If the gas pressure inside the cell 15A were to double, the molecular density therein would also double, and the measured concentration value would also double. Therefore, in order to perform accurate concentration measurements, it is necessary to maintain the gas pressure within the cell constant. In the embodiment of the present invention, the atmosphere open pipe 17 must be used in order to send the gas exiting the cell 15A to the semipermeable membrane vapor phase dehumidifier as a dry gas for purging, without directly dissipating it into the atmosphere as in the conventional case. For example, the gas pressure inside the cell 15A may fluctuate, and accurate temperature measurement cannot be expected. Therefore, by using a tube open to the atmosphere, the gas pressure inside the cell is maintained at a constant pressure of approximately atmospheric pressure, thereby ensuring the accuracy of concentration measurement in the analyzer 15. As explained above, according to the present invention, in a conventional gas analysis device consisting of one analyzer, an expensive indwelling tank or the like is not required, and in addition to providing an atmosphere opening pipe, it is possible to simply install a gas flow path. This method has the advantage that the water content of the reference gas and the sample gas can be equalized by simply adding a means for switching between them, making it possible to measure concentration with less error.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a semipermeable membrane vapor phase dehumidifier, and Figure IA is a cross-sectional view of a semipermeable membrane vapor phase dehumidifier.
In the figure, a cross-sectional view taken along the line FIG. In the figure, 1 is the outer tube, 2 is the partition plate, 3 is the inner tube, 4 is the inlet, 5 is the outlet, 6 is the inlet, 7 is the outlet, 8 is the gas sampling probe, 9 is the NH3 converter, 10 is the N2 Converter, 11 is also an N〇2 converter, 12 and 12a are semipermeable membrane gas phase dehumidifiers, 13 is a pump, 14 is a fusuma valve, 15 is an infrared gas analyzer, 16 is a pump, 17 is an atmosphere open pipe,
18 indicates a switching valve. Sea prisoner★IA cause★2 drawings 3 bacteria o 4 drawings

Claims (1)

[Claims] 1. First and second semipermeable membrane gases capable of passing water vapor in the wet gas and purging it to the outside by flowing wet gas inside the semipermeable membrane and flowing dry gas for purging to the outside. a phase dehumidifier, one cell through which gas can flow and receives light irradiation, a gas dehumidified by the first dehumidifier (first gas), and a gas dehumidified by the second dehumidifier. (a second gas); a first gas flow path switching means that alternately switches and flows a second gas to the cell;
Measure and store the amount of transmitted light when the gas is flowing,
means for comparing temporally adjacent measured values; an atmosphere-opening tube with one end open to the atmosphere for receiving the gas that has passed through the cell and maintaining it at a substantially constant pressure; and an exhaust gas into the open tube. When the exhausted exhaust gas corresponds to the first gas, the exhaust gas is sent to the second dehumidifier and the second dehumidifier.
When the gas corresponds to the gas, the exhaust gas is passed to the first dehumidifier as a purge dry gas, and the gas that was not switched to the cell side by the first gas flow path switching means is When the gas corresponds to the first gas, the gas is supplied to the second dehumidifier, and when the gas corresponds to the second gas, the gas is also supplied to the first dehumidifier as a purge dry gas. A gas analyzer comprising: a second gas flow path switching device that switches in synchronization with the first gas flow path switching device.