In the upper column fractionation, below the liquid air inlet is called the stripping section, and above the liquid air inlet is called the distillation section. The stripping section realizes the separation of oxygen and argon, and the distillation section realizes the separation of oxygen and nitrogen. Because the boiling points of oxygen and argon are relatively close, the separation is difficult. In order to ensure the purity of oxygen, the separation of oxygen in the distillation section is not clean, and argon escapes with oxygen and nitrogen. If high purity nitrogen is to be obtained, argon will condense with oxygen in the distillation section, which will affect the purity of oxygen. In order to ensure the purity of oxygen and obtain high purity nitrogen, it is necessary to extract part of the gas with high argon concentration in the distillation section.
