JPS6010256B2 - 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, infrared gas analyzers utilize the fact that molecules with dipole moments absorb infrared rays at wavelengths unique to each molecule, creating transitions between their vibrational energy levels. The concentration can be measured by introducing a sample gas into the sample cell and measuring the attenuation rate of the infrared rays transmitted through the sample cell at a wavelength that is absorbed by the molecules whose concentration is to be measured in the sample gas. However, if the sample gas contains moisture,
Since water has the property of absorbing infrared rays over a relatively wide range of wavelengths, the infrared wavelengths absorbed by the molecules whose concentration in the sample gas is to be measured tend to overlap with the infrared wavelengths absorbed by the water. Even if the attenuation rate of infrared rays of the relevant wavelength is measured, a concentration measurement 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, and both the sample and reference cells are A method to measure the difference in transmitted light is being explored. 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, NH3 in the sample gas is converted to nitric oxide (NO) using a thermal converter, and the sum of the NO originally present in the sample gas and the converted NO is absorbed by the first infrared absorption. On the other hand, the sample gas still containing N& is passed through the second same cell, and the N 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 NH3
Concentrations do not include errors due to moisture. 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 fog point temperature of the gas at the outlet of the dehumidifier is set to 1 to
It is controlled at 3 degrees Celsius, and it is impossible to lower the dew point temperature any further due to freezing. On the other hand, the latter semi-permeable membrane vapor phase dehumidifier can relatively easily dehumidify up to a fog point temperature equivalent to -20 oo. If the degree of dehumidification is low and the sample gas contains a lot of moisture, the optical system of analytical instruments such as infrared analyzers will become more contaminated.
This can cause zero point drift in the indicator, and in the case of a chemiluminescent analyzer, it can cause a span! Wake up J-futo,
This hinders accurate analysis value indication. Therefore, it can be said that a semipermeable membrane vapor phase dehumidifier with a high dehumidifying capacity is superior to an electronic gas cooler with a poor dehumidifying capacity. FIG. 1 is a cross-sectional view of such a semipermeable membrane vapor phase dehumidifier, and FIG. IA is a cross-sectional view taken along the line x--X' in FIG.

See these figures. The semipermeable membrane vapor phase dehumidifier is composed of an outer tube 1 and a large number of inner tubes 3, 3, 3 supported inside the outer tube 1 via partition plates 2, 2, and each inner tube 3 has a ~
EI DuPont's product name Nafion (NAFI)
It is composed of a compound called ON) and has the function of selectively permeating only water vapor from the inside to the outside through the pipe wall. Now, wet sample gas containing water vapor is introduced into each inner tube 3 from the inlet 4 and the outlet 5
When dry gas for purging is passed through the outside of the inner tube 3 from the other inlet 6 toward the outlet 7 while discharging the wet sample gas, water vapor in the wet sample gas passes through the wall of the inner tube 3 and is purged to the outside. be done. A semipermeable membrane vapor phase dehumidifier has the configuration and functions described above, and is used in a gas separation device for the reasons described above.

On the other hand, the present applicant has already proposed a highly sensitive analyzer, such as an infrared ammonia gas (NH3) analyzer, that can detect a significant ammonia gas concentration.

The analysis device according to this proposal includes a first cell irradiated with infrared light, a second cell also irradiated with infrared light, and each infrared light transmitted through each of the first and second cells. A detector for detecting the east quantity, and a sample gas to be analyzed and a reference gas to be compared are periodically switched and flowed simultaneously through the first cell and the second cell. By appropriately processing the electric signal obtained from the detector when the sensor is set, it is possible to measure the concentration of the sample gas with high sensitivity. An important point in the gas analyzer according to this existing proposal is that the sample gas and reference gas are alternately switched to flow through the first cell and the second cell. In addition to its high sensitivity, it has excellent advantages such as eliminating the possibility of objects contaminating only either the sample side or the reference side of the infrared optical system, so there is no zero point drift in the concentration indicator. It is. Now, FIG. 2 shows an outline of the configuration of a conventional analyzer when the above-mentioned semipermeable membrane vapor phase dehumidifier is used in the previously proposed analyzer.

Refer to the same figure. Sample gas collected by sampling probe 8 (for example, 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 valve 14. Infrared gas analyzer 1 via b
After passing through the first cell i5A of 5, it is dissipated into the atmosphere. Further, as a second flow path for the sample gas sampled by the probe 8, the sample gas first passes through the N02 converter 11, where N02 in the sample gas is converted to NO. Therefore, the sample gas containing the N ratio and NO is
After being dehumidified at 2a, it is sucked into the pump 13a, passes through the inlet d and outlet c of the switching valve 14, passes through the second cell 15B of the infrared gas analyzer 15, and is then released into the atmosphere. In the infrared gas analyzer 15, a first cell 15A and a second cell 15B are arranged spatially in parallel, and in front of them is a chopper 1 (not shown) driven by a motor.
58 are disposed, so that the cells 15A, 15B are alternately irradiated with infrared wavelength light from the light sources 15C, 15D. A detector 15F is arranged behind both cells 15A and 15B to detect the difference in the amount of infrared absorption between both cells. In the current example, the first
Since the second cell 15A contains a gas that does not contain an N ratio, and the second cell 15B contains a gas containing NH3, the detector 1
The difference in the amount of infrared absorption detected by No. 5 is due to the presence of NH3, and in this way the concentration of N can be measured. Next, the switching valve 14 switches the gas flow path. A reference gas not containing NH3 is sucked by the pump 13 and led to the second cell 158 of the gas analyzer 15 from the inlet a of the switching valve 14 through the outlet c, and a sample gas containing N is drawn by the pump 13a. It is sucked and the switching valve 1
4 is led to the first cell 15A of the gas analyzer 15 via the outlet b. In this way, by periodically switching the gas flow path using appropriate means in the switching valve 14, the reference gas that does not contain NH3 and the sample gas that contains NH3 are alternately flowed into the first cell 15A of the gas analyzer 15. , the sample gas containing NQ and the reference gas not containing NQ are alternately flowed into the second cell 15B, and the electrical signals obtained from the detector 15F are appropriately controlled under the condition where they are alternately switched at a constant cycle. The treatment enables highly sensitive detection of NH3 concentration. Semipermeable membrane vapor phase dehumidifier 12, 12
As the purge dry gas used in step a, clean dry air (referred to as instrumentation air) prepared separately was used, and this was sucked by the pump 16 and was suitable for the outside of the inner pipe of the dehumidifiers 12 and 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 sample gas and the purge dry gas, etc. In order to solve this problem, in the past it was necessary to take measures such as placing the dehumidifier itself in a cryogenic chamber to maintain a constant gas pressure, which resulted in high costs. This invention was made in order to eliminate the drawbacks of the prior art as described above, and an object of the invention is to eliminate the mist of each gas at the outlets of both dehumidifiers without using an expensive temperature tank. To provide a highly sensitive gas analyzer as 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. mutually used as a gas,
The purpose is to equalize the dew point 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 semipermeable membrane vapor phase dehumidifier 12, sucked by the pump 13, and
The gas enters the first 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 directly dissipated into the atmosphere, but passes through the atmospheric dissipation tube 17 and then into the second switching In the 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, it is dehumidified by the semipermeable membrane vapor phase dehumidifier 12a, sucked by the pump 13a, enters the second cell 15B of the infrared gas analyzer 15 through the inlet d and outlet c of the switching valve 14, and exits the cell. Similarly, the gas is also supplied as a purge dry gas to the membrane vapor phase dehumidifier 12 on the semi-opposite side via the atmospheric diffusion pipe 17a and from the inlet d to the outlet c of the second switching valve 18. When the gas flow path is switched in the switching valve 14 and the gas dehumidified by the dehumidifier 12 enters the second cell 16B in the gas analyzer 15 through the inlet a and outlet c in the switching valve 14, If the second switching valve 18 also switches the gas flow path in synchronization with the first switching valve 14, the gas leaving the cell 15B will be transferred to the inlet d of the switching valve 18,
It is also supplied as purge dry gas to the dehumidifier 12a on the opposite side via the outlet b. 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 so as to have a more negative pressure than the sample gas, the water vapor partial pressure in the sample gas is ultimately higher than that of the purge dry gas.

Therefore, the sample gas is dehumidified in the dehumidifier 12 or 12a. In a semipermeable membrane vapor phase dehumidifier, the fog point temperature of the gas at its outlet varies depending on the dew point temperature of the purge drying gas. In addition, there is often some variation in the product. According to the embodiment of the present invention, when the dehumidification capacity of the first dehumidifier on one side is high (the fog point of the outlet gas is low),
As a result, the dehumidified gas is supplied to the second dehumidifier on the other side as purge dry air, thereby increasing the dehumidification capacity of the second dehumidifier (lowering the dew point). On the other hand, the second
The gas with a higher dew point than that of the dehumidifier is
Since the first dehumidifier is used as a purge dry gas for the first dehumidifier, the dehumidification capacity of the first dehumidifier is reduced. In this way, eventually
The dehumidification capacities of the first and second dehumidifiers are equalized, and the fog point temperatures of the gases dehumidified by both dehumidifiers are not close to the same value.
That's why. Next, in Fig. 3, infrared gas analyzer 1
The gas emitted from each cell 15A, 15B of 5 is connected to the atmosphere release pipe 1
Let me explain the reason for passing 7.17a.

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 entrance 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 gas exiting the cells 15A and 15B is not directly dissipated into the atmosphere as in the conventional case.
Furthermore, in order to send the dry gas for purging to the semi-permeable membrane vapor phase dehumidifier, the cell 15
The gas pressure inside A and 15B may fluctuate, and accurate concentration 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. FIG. 5 shows the second embodiment of this invention.
FIG. 2 is a schematic configuration diagram showing an embodiment of the present invention. Comparing this figure with Fig. 3, one differential type analyzer 15 is used in Fig. 3, while in Fig. 5 two ordinary analyzers (15 ', 15'') Since the mode of operation is exactly the same except that it is used, there is no need to further explain Fig. 5.As explained above, this According to the invention, in a conventional high-sensitivity gas analyzer, the reference gas and the sample gas can be exchanged by simply providing a tube open to the atmosphere and adding a means to switch the gas flow path, without requiring an expensive oak temperature tank or the like. This has the advantage of equalizing the moisture content of the water and making it possible to measure concentration with less error.

In each of the embodiments shown in FIGS. 3 and 5, the pumps 13 and 13a are placed after each dehumidifier 12 and 12a, but if the pump is placed in front of the dehumidifier, Compared to the above, since there is no generation of condensed water (drain) due to the compression of gas accompanying pressurization of the pump, there is also the advantage that the valve in the pump does not deteriorate due to condensed water and its life is extended.

[Brief explanation of the drawing]

Figure 1 is a sectional view of a semi-permeable gas phase dehumidifier, and Figure IA is a cross-sectional view of a semi-permeable gas phase dehumidifier.
In the figure, a cross-sectional view taken along the line FIG. 5 is a schematic diagram showing a second embodiment of the present invention. 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, 1 is the An N02 converter, 12 a semipermeable membrane gas phase dehumidifier, 13 a pump, 14 a switching valve, 15 an infrared gas analyzer, 16 a pump, 17 an atmosphere open pipe, and 18 a switching valve. Figure 1 Figure IA Figure 2 Figure 3 Figure 4 Figure 5

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, first and second cells through which gas can flow and receive light irradiation, and gas dehumidified by the first dehumidifier and gas dehumidified by the second dehumidifier. a first gas flow path switching means that alternately causes gas to flow through the first cell and the second cell at the same time; and means that measures the amount of light transmitted through each of the first and second cells during gas flow; first and second atmosphere opening pipes each having one end open to the atmosphere and for exhausting the gas that has passed through each of the cells and maintaining the pressure at a substantially constant pressure; and the first and second atmosphere opening pipes. When the exhaust gas discharged into the pipes corresponds to the gas dehumidified by the first dehumidifier, it is transferred to the second dehumidifier, and the exhaust gas corresponds to the gas dehumidified by the second dehumidifier. and a second gas flow path switching means for switching the flow of the exhaust gas in synchronization with the first gas flow path switching means so as to flow the exhaust gas to the first dehumidifier as purge dry gas. A gas analyzer characterized by comprising: