The tower device through its internal components to gas (vapor) - liquid and liquid - liquid phase between the full contact for mass transfer and heat transfer. Through the tower equipment to complete the unit operation are usually: distillation absorption, desorption, extraction, etc., can also be used for medium cooling, gas purification and drying and humidification. Tower tower according to the operating pressure is divided into: pressure tower, pressurized tower; according to the production unit is divided into: absorption tower, distillation tower, extraction tower, drying tower, washing tower; according to the tower structure is divided into: Packed tower