The basic function of the distillation column of the air separation unit is to form a phase interface in which the gas-liquid two phases are in full contact, so that the mass and heat transfer can be carried out quickly and effectively, and the gas-liquid two phases after contact mixing and mass transfer can be separated in time without entrainment.
Classification of distillation columns: there are many kinds of distillation columns. According to the contact mode, they can be divided into continuous contact (packed column) and step-by-step contact (plate column). They are widely used in absorption and distillation operations.
1、 Packed tower: a certain height of packing is filled in the cylindrical shell, the liquid is evenly distributed on the top of the packing layer through the tower top spray device, flows through the packing layer from top to bottom along the packing surface by gravity, and then is discharged from the tower bottom; The gas is pushed by the pressure difference through the gap of the packing layer and flows from one end of the tower to the other end. The gas and liquid contact on the packing surface for mass and heat exchange, and the composition of the two phases changes continuously along the tower height.
2、 Plate tower: several layers of trays are horizontally arranged in the cylindrical shell at a certain distance. The liquid flows through each layer of trays from top to bottom by gravity and is discharged from the tower bottom. A certain thickness of flowing liquid layer is maintained on each layer of trays; Driven by the pressure difference, the gas successively passes through the liquid layer on each tray from the bottom of the tower to the top of the tower for discharge. Gas and liquid contact plate by plate in the tower for mass and heat exchange, so the composition of the two phases changes step by step along the tower height.
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