JPS63228052A - Detecting method for impure gas - Google Patents

Abstract

PURPOSE:To correctly detect impure gas by setting detection temperature above specific temperature and detecting the heat conductivity of measured gas in the purification of gaseous hydrogen by a low temperature adsorption gas purifying method. CONSTITUTION:An adsorption cylinder 10 which is filled with a molecular sieve, etc., is provided in a refrigerant tank 11. Raw material gas 14 is supplied to the adsorption cylinder 10 to adsorb the impure gas at low temperature and purified gaseous hydrogen is led out of an exit 17 to a rundown pipe 15. Further, a reference side pipe 2 and a sample side pipe 3 are provided in a heat conductivity detector 1, the purified gaseous hydrogen is supplied from the rundown pipe 15 to the reference side pipe 2, and the measured gas is supplied from a measurement point 18 nearby the exit 17 in the adsorption cylinder 10 to the sample side pipe 3. Then the detection temperature is raised by a heater 4 to >=200 deg.C to detect the difference in conductivity between the reference side pipe 2 and sample side pipe 3, thereby detecting impure gas such as N2, O2, and CO in the measured gas. Thus the detection temperature is raised to >=200 deg.C, so the mixing of the impure gas is accurately detected without being affected by variation in heat conductivity.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method and apparatus for detecting impure gas, and more particularly to a method for detecting impure gas contained in hydrogen gas being purified by cryogenic adsorption. .

With the development of the semiconductor industry, nuclear power industry, etc., the demand for various gases such as hydrogen and helium is increasing, and the gases used in these fields are required to be extremely gentle. However, these commercially available gases usually contain impure gases such as nitrogen, carbon oxide, and methane, so it is necessary to remove these impure gases, and various gas purification devices have been introduced. There is. One of the representative examples of these is a cryogenic adsorption gas purification device that adsorbs and removes impurity gas at extremely low temperatures using an adsorption cylinder filled with an adsorbent. and Japanese Unexamined Patent Publication No. 61-18616.

These devices basically consist of an adsorption cylinder, a refrigerant tank, a heat exchanger, a heating device, etc., and are capable of adsorption purification of gas at extremely low temperatures using liquid nitrogen as a refrigerant, and regeneration of adsorbents by heating. are performed alternately. In such cryogenic adsorption gas purification equipment, during gas purification, as the adsorption of impure gas progresses, the adsorption zone of impure gas sequentially moves from the upstream side to the downstream side of the adsorption column, and finally the adsorption layer impure gas is mixed into the purified gas discharged from the outlet of the adsorption column.

For this reason, it is necessary to take measures such as predicting the breakthrough of the adsorption layer and switching to another adsorption column before the breakthrough occurs. Therefore, it is extremely important to detect impure gas.

[Conventional technology]

Conventionally, the method for detecting impurity gases contained in gases such as hydrogen and helium is to analyze the sample gas extracted from the adsorption column at predetermined intervals using a mass spectrometer, infrared analyzer, gas chromatograph, etc. It was common. However, analysis using these analyzers is an intermittent method, which is not only time-consuming, but also requires time to obtain results, which has the disadvantage that impure gases cannot be detected quickly.

In contrast, the present inventors first developed a method of detecting impure gas by using a thermal conductivity detector, flowing purified gas and measurement gas through it, and detecting the difference in thermal conductivity between the two. After further consideration, we proposed that the measurement gas or purified gas be passed to the control side of the thermal conductivity detector, and the measurement gas and purified gas should be alternately switched to flow to the sample side. A method has been disclosed in which the incorporation of impure gas is monitored while correcting the deviation of the 00 point on the sample side, thereby detecting trace amounts of impure gas with higher sensitivity and more quickly (Japanese Patent Laid-Open Publication No. 130864/1986).

[Problem to be solved]

This method using a thermal conductivity detector can be widely applied to detecting impurity gases such as hydrogen gas and helium.

The detection part of the thermal conductivity detector has a built-in self-tarder, but the heating temperature is usually set at 50 - 50℃ to increase the sensitivity.
It is used at a relatively low temperature of 100°C.

However, in the purification of hydrogen gas by the cryogenic adsorption gas purification method described above, when the sample hydrogen gas derived from the purification system is set at 50 to 100°C on the thermal conductivity detector, these hydrogen gases are Even when no impure gas is contained, the thermal conductivity not only shows a value different from that of normal hydrogen gas, but also changes in the thermal conductivity due to fluctuations in the gas flow rate in the purification system, the extraction position of the sample gas, etc. A phenomenon occurs in which the temperature fluctuates greatly. For this reason, even if the thermal conductivity changes due to impure gas mixed into hydrogen gas, it is difficult to distinguish whether the change is due to impure gas or not, and especially when the concentration of impure gas is low, it cannot be detected at all. There was a point.

[Means for solving problems]

The inventors of the present invention have conducted intensive research to solve these problems and reliably detect impurity gases for hydrogen gas in cryogenic adsorption gas purification in the same way as for other gases.
The inventors discovered that the above-mentioned change in thermal conductivity can be prevented by flowing sample hydrogen gas while the heating temperature of the detection part of the thermal conductivity detector is set at a high temperature, and the present invention was completed.

That is, the present invention provides a method for detecting impure gas, in which impurity gas contained in hydrogen gas being purified is detected by a thermal conductivity detector using a cryogenic adsorption gas purification apparatus equipped with an adsorption column filled with an adsorbent. By flowing the purified gas and the measurement gas led from the adsorption column through the thermal conductivity detector with the heating temperature of the detection part set to 200°C or higher, and detecting the difference in thermal conductivity between the two. This is an impure gas detection method characterized by detecting impure gas in a measurement gas.

The present invention is applied to the detection of impurity gases such as nitrogen, oxygen, carbon oxide, carbon dioxide, and methane contained in hydrogen gas being purified by a cryogenic adsorption gas purification device, and a thermal conductivity detector is used. .

The cryogenic adsorption gas purification device to which the present invention is applied is equipped with an adsorption cylinder, a refrigerant tank, a heat exchanger, a heating device, etc., and usually has two series of adsorption cylinders, one in which adsorption purification is performed. On the other hand, the adsorbent is regenerated by heating. The adsorption cylinder is composed of one or more cylinders, and the inside thereof is filled with an adsorbent such as activated carbon or molecular sieve. When refining hydrogen gas, it is cooled with liquid nitrogen, and impurity gas is adsorbed and removed by flowing the raw hydrogen gas at an extremely low temperature of about -196°C to obtain purified gas, but as the adsorption of impure gas progresses, the adsorption zone The gas sequentially moves from the upstream side to the downstream side of the adsorption cylinder, and finally the adsorption layer is broken and impure gas is mixed into the purified gas. For this reason,
It is necessary to perform operations such as switching to another adsorption column whose adsorbent has been regenerated before breakthrough.

In the present invention, the adsorption cylinder is provided with a measurement point for extracting the measurement gas. Usually, the measuring point is located upstream from the outlet of the adsorption cylinder, at a position where impurity gas detection can provide enough time for switching to another adsorption cylinder before the adsorption layer breaks through. Furthermore, in the case of an adsorption cylinder in which a large number of cylinders are connected in series through connecting pipes, the measurement point can be provided at the connecting pipe connecting the most downstream cylinder and its upstream cylinder.

The thermal conductivity detector used in the present invention basically has a bridge circuit made of metal wire resistance and has two gas flow paths.
One side is the control side, and the other side is the sample side, and a gas containing no impurity gas is passed through the control side, and a test gas is passed through the sample side, and the difference in thermal conductivity between the two is measured using a platinum wire. The impure gas in the sample gas is detected by extracting the potential difference due to the difference in electrical resistance.

In the present invention, purified hydrogen gas is normally flowed to the control side, and measurement gas led from the measurement point of the adsorption cylinder is flowed to the sample side, and impure gas is detected by a change in the thermal conductivity difference between the two.

Note that purified hydrogen gas is usually introduced from the outlet of the adsorption cylinder, but it can also be introduced from other purification equipment or cylinders. In addition, the measurement gas is not diluted with a carrier gas or the impurity gases are separated unlike in a gas chromatograph, and the total concentration of the impurity gases is measured as is, so even trace amounts of impurity gases can be detected with high sensitivity. Although it can be detected,
Similar to the method in Publication No. 1-1308754, if a method is used in which the measurement gas and purified hydrogen gas are alternately passed through the sample side and the potential difference with drift corrected is detected, impurity gas can be detected with even higher sensitivity and accuracy. Can be detected.

In the present invention, the temperature of the detection part of the thermal conductivity detector is set to 200
If the set temperature at which the purified hydrogen gas and measurement gas are flowed is lower than 200°C while being set at a high temperature of 230 to 400°C, the hydrogen gas may interact with the adsorbent in the purification process, It is assumed that this is caused by temperature and flow rate fluctuations. The thermal conductivity of the hydrogen gas itself changes, making it impossible to accurately detect impure gas.

In the present invention, the control side and sample side of the thermal conductivity detector are connected to sample tubes for purified hydrogen gas and measurement gas, respectively.

Next, the present invention will be specifically explained with reference to the drawings.

FIG. 1 is a flow sheet in which a thermal conductivity detector used in the present invention is connected to a cryogenic adsorption gas purification device through a sample tube.

In FIG. 1, a thermal conductivity detector 1 includes two sample gas channels on a control side 2 and a sample side 3, a detection section 5 having a heater 4 for temperature setting, a recorder 6, and an alarm 7.
It consists of

Constant flow valves 8 and 9 are provided at the inlets of the channels on the control side 2 and sample side 3 of the thermal conductivity detector 1, respectively.

On the other hand, in a cryogenic adsorption gas purification device (only one series is shown), a refrigerant tank 11 containing an adsorption column 1 ( ) filled with an adsorbent is used.
is housed in a vacuum insulation container 13 together with a heat exchanger 12,
A raw material gas supply pipe 14 and a purified gas withdrawal pipe 15 are guided to this, and are connected via a heat exchanger 12 to an inlet 16 and an outlet 17 of the adsorption cylinder 1 () in the refrigerant tank 11, respectively. It constitutes one line of the purification system. A measurement point 18 is provided at a position closer to the gas upstream side from the outlet 17 of the adsorption cylinder 1 ( ). The measurement point 18 is connected to the constant flow valve 9 by a sample pipe 20, and the sample pipe 19 branched from the purified gas extraction pipe 15 is connected to the constant flow valve 8, and at the same time, the sample pipe 19 is connected to the constant flow valve 9 by a bino gas pipe 21. is also guided. Valve 22 is provided in sample tubes 19 and 20 and bypass tube 21.
a, 22b and 22c, respectively.

When refining hydrogen gas, the refrigerant tank 11 is filled with liquid nitrogen, and hydrogen gas is supplied from the raw material gas supply pipe 14 while the adsorption column 1 ( ) is cooled to an extremely low temperature. This hydrogen gas is pre-cooled by a heat exchanger 12, enters the adsorption column 1 () from an inlet 16 in the refrigerant tank 11, and is purified by adsorbing and removing impurity gas there. The purified hydrogen gas passes through the outlet 17 and the heat exchanger 12, and is extracted from the purified gas extraction pipe 15.

On the other hand, detection of impure gas is performed as follows.

First, after setting the heater 4 of the detection unit 5 to a predetermined temperature (200°C or higher), the sample tube 19 and the bypass tube 21
Open the valves 22a and 22c to flow purified hydrogen gas to the control side 2 and sample side 3, respectively, via the constant flow valves 8 and 9.
Adjust to V. Next, close the valve 22c of the bypass pipe 21,
The valve 22b of the sample tube 20 is opened to switch the sample side 3 to the measurement gas, and the potential difference is continued to be monitored in this state. As time passes, adsorption of impure gas in adsorption column 1 () progresses 4
When the adsorption zone reaches the measurement point 18 and impure gas is mixed into the measurement gas, a significant change in potential difference occurs at this point, and the impure gas is detected.

In addition, when the impurity gas concentration in the raw material gas is particularly low,
It is necessary to increase the sensitivity of this potential difference, but in this case, slight changes in potential difference due to the drift of the thermal conductivity detector interfere, making identification difficult. In such a case, the sample side 3
By alternately switching the measurement gas and purified hydrogen gas to flow, it is possible to detect a slight change in potential difference and detect a trace amount of impure gas while correcting drift.

Changes in the potential difference are monitored by the recorder 6, the alarm 7, etc., but it is also possible to automatically switch the gas purification apparatus by operating a switching valve or the like using a signal from the alarm 7, for example.

〔Effect of the invention〕

According to the present invention, contamination of impure gas can be accurately detected without being affected by changes in thermal conductivity of hydrogen gas during the cryogenic adsorption gas purification process. In addition, the detection device is small and relatively inexpensive, and can be easily installed in purification equipment, making it possible to continuously monitor the contamination of impure gases.
Breakthrough of the adsorption tube can be reliably predicted. Furthermore, the operation of the purification apparatus can be automated by operating the switching valve of the adsorption column based on the detection signal from the alarm.

〔Example〕

Example 1 The structure was similar to that shown in FIG. 1, but instead of one tube, 2.5 kg of activated carbon was filled as an adsorbent.
omm) A cryogenic adsorption gas purification system with seven adsorption cylinders connected in series through connecting pipes removes impurities from the hydrogen gas being purified at a cryogenic temperature of approximately 2196°C and at a gas flow rate of 66 m2/hr. Gas was detected. Table 1 shows the results of gas chromatograph analysis of impurities in the raw hydrogen gas and purified hydrogen gas.

Table 1 N2 25 0.01 Below 02 4 0.02 ttCo
10 0.03 ttCOz
2 0.02 pCH490,03tt The measurement points for extracting the measurement gas are 6 from the upstream side of the adsorption column.
It was provided in the connecting pipe section that connected the tube opening and the 7th port (most downstream side).

Detection unit ([■ Shimadzu Corporation, TCD-7), recorder,
A thermal conductivity detector with an alarm was connected to the → Camphor tube led from the cryogenic adsorption gas purification device.

First, as a preliminary experiment, we attempted to measure thermal conductivity with the heater in the detection section set at 100° C., which is the normal heating temperature. First, purified hydrogen gas alone was flowed at 5 Q at /min to each of the control side and the sample side, and the potential difference between the two was set to 0. After adjusting to OOmV, when the sample side was switched to the measurement gas, a potential difference of about 0.24 mV appeared even though no impurity gas was mixed in, and this potential difference was ±
A phenomenon was observed in which vibration occurred with a width of about 0.04 mV. The results are shown in FIG.

In addition, when the raw material gas supply rate to the adsorption cylinder is intentionally increased (point a in Figure 2) or decreased (point in Figure 2), the potential difference changes drastically, and the gas to be measured is It has been shown that even if impure gas gets mixed in, it is difficult to identify it.

Next, as an example of the present invention, the difference in thermal conductivity was monitored in the same way as in the preliminary experiment when the temperature of the detection part was set at 280°C. The result is as in the example shown in FIG. 2, and as long as there is no impurity gas in the measurement gas, the potential difference is 0. OO
mV, and as in the preliminary experiment, no potential difference occurred even if the feed rate of the raw material gas to the adsorption column was increased (point a in Figure 2) or decreased (point in Figure 2). Furthermore, when I continued monitoring in this state, the result was 0.0 after 754 hours. The potential difference, which was OOmV, increased to 0.04mV (point C in Figure 2). At this point, the gas to be measured was analyzed using a gas chromatograph, and 12 ppm of nitrogen was detected, confirming that the adsorption zone of the adsorption cylinder had reached the measurement point.

Tests were also conducted when the set temperature was set to 230°C and 350°C, and both showed stable thermal conductivity similar to that at 280°C.
A potential difference of mV was created.

[Brief explanation of drawings]

FIG. 1 is a flow sheet in which a thermal conductivity detector is connected to a cryogenic adsorption gas purification device through a sample tube, and FIG. 2 is a diagram showing a potential difference curve appearing in the thermal conductivity detector. The drawing numbers are as follows. 1 Thermal conductivity detector 2 Control side 3 Sample side 4 Heater 10 Adsorption tube
18 Measurement points 19 and 2 () Sample tube 21 Bypass tube Patent applicant Nippon Bionics Co., Ltd. Representative Fumi Takasaki, attorney Patent attorney Sada Kobori Calculation/Figure time (H7=)

Claims (1)

[Claims] Detection of impure gas by detecting impurity gas contained in hydrogen gas being purified using a thermal conductivity detector using a cryogenic adsorption gas purification device equipped with an adsorption column filled with an adsorbent. In the method, the purified gas and the measurement gas guided from the adsorption column are passed through the thermal conductivity detector with the heating temperature of the detection part set to 200° C. or higher, and the difference in thermal conductivity between the two is detected. A method for detecting impure gas, characterized by detecting impure gas in a measurement gas.