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How does the DEAR air separation unit analyze the purity of nitrogen?
2022-01-07

The boiling point of 0.932% argon in the air is between oxygen and nitrogen, and the content is the highest in the middle of the upper column of the DEAR air separation unit, which is called argon fraction. At the same time of separating oxygen and nitrogen, the argon fraction is extracted for further separation and purification, and the argon by-product can also be obtained. For all low pressure air separation units, 30% - 35% argon in the process air can be obtained as a product (the latest process has increased the argon extraction rate to more than 80%);The main components of air are oxygen and nitrogen, which exist in molecular state respectively. Molecules are the smallest particles that keep their original properties. The order of magnitude of their diameter is 10-3cm. The number of molecules is very large and they are constantly moving irregularly. Therefore, oxygen, nitrogen and other molecules in the air are evenly mixed with each other. It is difficult to separate them. At present, there are three main separation methods.
Nonferrous metal smelting. Pyrometallurgy is the most important method in heavy metal smelting. In addition to sulfur and iron oxidation, it also depends on fuel combustion to provide heat. In order to strengthen the smelting process, reduce energy consumption and harmful flue gas, oxygen enrichment instead of air is used for smelting, and the production capacity of the equipment can be improved.If you want to increase the output of liquid products and open one more expander in normal production, it is OK only from the perspective of cold balance, but too much expansion air into the upper tower will destroy the distillation condition of the upper tower and reduce the extraction rate of low oxygen. At the same time, taking more liquid will also affect the working condition of the heat exchanger in the tower and the reflux ratio of the distillation tower, so it is also limited.It has been widely used in large and medium DEAR air separation plants. The plate unit is generally arranged in a vertical star shape. Because the height of plate unit is limited by safety, the heat exchange area that can be arranged in the range of tower diameter is limited, and the double-layer or multi-layer (four layer) star arrangement is used in large DEAR air separation units.
If the resistance of the cold section increases, it is carbon dioxide freezing; if the resistance of the hot section increases, it is water freezing; if the resistance of the whole heat exchanger increases, it is both freezing, or molecular sieve powder is blocked; the abnormal operation of the refrigerator causes the temperature of the chilled water to rise, and the air cannot be cooled to the normal temperature.With the development of large-scale air separation plant, the heat transfer area of the main condensing evaporator is also increasing. If the tube type is used, the number of tubes will be more than 20000, which brings great difficulties to the manufacturing. At present, the plate fin type has been completely replaced.The acetylene content in liquid air and liquid oxygen needs to be analyzed every day, so the liquid air and liquid oxygen discharge valves have to be operated every day. It is easy to open the valve, but difficult to close it. Sometimes it can't be closed at all. This is mainly because there is water in the valve stuffing box.