Monitoring of oxygen content in gas during production of industrial gas and high purity gas
In the production process of industrial gas and high-purity gas, the monitoring of oxygen content in the gas is an important issue. This is because oxygen is a chemically active substance and the most oxidizing oxidant.
In some industries, when people need it as an oxidant, they hope that the higher the purity, the better; conversely, in other industries, the presence of oxygen in other gases is a harmful substance, and people want the oxygen content to be less The better. Therefore, the range of oxygen content in various gases is a matter of great concern.
There are many methods for detecting oxygen content, but the methods for detecting oxygen content according to the standards specified in the gas standards are chemical and electrochemical. This is because only the chemical method and the electrochemical method can accurately determine the oxygen content in the gas.
Some units use a gas chromatograph as the detection method for various gas components, and can also detect the oxygen content in various gases. However, it must be pointed out that the value of the oxygen content detected by the gas chromatograph is usually the sum of the oxygen and argon (except for the gas chromatograph where argon is the carrier gas), in fact it is not just the value of oxygen. This is because it is difficult to separate oxygen and argon using the gas chromatography separation method under normal conditions, and the obtained oxygen peak data already contains the argon content. If you want to completely separate oxygen and argon, it is difficult in the gas chromatography separation method, but it is not not feasible. In fact, for accurate data and convenient operation, the gas standard stipulates that the detection of oxygen content in the gas should be based on the chemical method and the electrochemical method.
When performing oxygen content analysis, especially trace oxygen analysis, the oxygen content in the air is as high as 21% O2, so if not handled properly, it is easy to cause pollution and interference to the sample, and the analysis result data is incorrect. The main reason is the improper operation of the instrument. Only a few factors affecting the measurement are discussed below.
1. Leakage. The oxygen analyzer must be strictly leak-detected before it is first used. The instrument can obtain accurate data results only under strict premise. Any connection points, welding points, valves, etc. are not tight, which will cause the oxygen in the air to penetrate into the pipeline and the inside of the instrument, resulting in a high oxygen content.
2. Pollution. When reusing the instrument, first pay attention to whether there is air leakage when connecting the sampling line, and carefully blow out the air leakage, and try not to let a large amount of oxygen pass through the sensor to extend the life of the sensor. In the process of purifying the pipeline system, in order to shorten the purification time, a certain method is required. Generally, high-pressure deflation and small flow blow-off are used alternately to rapidly purify the pipeline.
3. Selection of pipe material. Pipe material and surface roughness will also affect the change of oxygen content in the sample gas. Generally, it is not suitable to use plastic pipes or rubber pipes as connecting pipes. Usually copper or stainless steel tubes are used. For ultra-micro analysis (referring to <0.1ppm), polished stainless steel tubes must be used.
4. Simplification and cleanliness of the gas circuit system. Microanalysis requires that all kinds of pipe fittings, valves, meter heads, etc. in the gas path must be effectively excluded from the pollution caused by the sample gas. Therefore, the gas path system should be simplified as much as possible, and connectors with small dead angles should be selected. In addition, avoid the use of water seals, oil seals and wax seals to prevent pollution from escaping from dissolved oxygen. It is also necessary to avoid adding pollution-prone purification equipment to the pipeline from the sample gas to the instrument inlet. Only in this way can the system be clean and the data obtained be accurate.
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