The lower and upper columns are the main equipment in the distillation system of cryogenic oxygen air separation plant. The lower column and the upper column separate the components of the mixture gas into different components with the required purity by using the different boiling points. The upper and lower columns are of cylindrical structure. The lower column is equipped with multi-layer sieve plates, and the sieve plate is equipped with overflow bucket. There is an overflow baffle with dense holes. The upper column is equipped with regular packing and liquid distributor. In the distillation process of the lower column, the liquid flows through each sieve plate one by one from top to bottom. Due to the effect of overflow weir, a certain height of liquid level is created on the pedal. When the gas passes through the small hole of sieve plate from bottom to top, it contacts with the liquid and produces bubbles, which increases the gas-liquid contact area and makes the heat and mass exchange process efficient. The low boiling point components gradually evaporate and the high boiling point components gradually liquefy In the distillation process of the upper column, the gas passes through the distributor and rises along the packing plate. The liquid is evenly distributed on the packing plate through the water separator from top to bottom. On the surface of the packing, the gas and liquid are fully contacted for efficient heat and mass exchange. The oxygen content of the rising gas with low boiling point is continuously increased, and the high boiling point component oxygen is washed down to form reflux liquid. Finally, pure nitrogen with low boiling point is obtained at the top of the column and liquid oxygen with high boiling point is obtained at the bottom of the column.
