According to the structure, the tower can be divided into two categories: plate tower packed tower.

　　There are a certain number of trays in the tray tower, the gas contacts with the liquid layer on the tray in the form of bubble jet to transfer the substance. According to the gas-liquid operation state, it can be divided into bubbling tray, such as float valve, bubble cap, sieve plate jet tray, such as mesh, tongue other trays. It can also be divided into overflow tray (bubble cap, etc.) through flow tray (through flow grid plate, through flow sieve plate, etc.) according to whether there is downcomer .

　　The packing tower is equipped with a certain height of packing, the liquid flows top to bottom along the packing, the gas contacts with the liquid membrane bottom to top to carry out material transfer. It is often used in distillation, water absorption, extraction other operations. According to the structural characteristics, it can be divided into random packing (step ring, ball ring other granular packing) regular packing (mesh corrugated packing corrugated plate packing)

　　The packing tower is a mass transfer equipment which uses the packing in the tower as the contact component between gas liquid. The tower body of the packed tower is a vertical cylinder, the bottom is equipped with a packing support plate. A packing pressing plate is installed above the packing to prevent it being blown by the rising air flow. Liquid is sprayed on the packing the top of the tower through the liquid distributor flows down the packing surface. The gas is sent the bottom of the tower distributed by the gas distribution device (generally, there is no gas distribution device in the small diameter tower), then it flows continuously through the gap of the packing layer as a counter current with the liquid. On the surface of the packing, the gas-liquid two-phase contact closely for mass transfer. The packed tower is a continuous contact gas-liquid mass transfer equipment. The two-phase composition changes continuously along the tower height. Under normal operation, the gas phase is continuous phase the liquid phase is dispersed phase. When the liquid flows down the packing layer, it tends to concentrate on the tower wall gradually, which makes the liquid flow near the tower wall increase gradually. This phenomenon is called wall flow. The wall flow effect results in the uneven distribution of gas liquid phases in the packing layer, which leads to the decrease of mass transfer efficiency. Therefore, when the packing layer is high, it needs to be segmented redistributed in the middle. The liquid redistributor consists of liquid collector liquid redistributor. The liquid flowing the upper packing is collected by the liquid collector sent to the liquid redistributor. After redistributing, the liquid is sprayed on the lower packing. Packed tower has the advantages of large production capacity, high separation efficiency, small pressure drop, small liquid holding capacity large operation flexibility. The packing tower also has some shortcomings, such as high packing cost; when the liquid load is small, it can effectively wet the packing surface, so that the mass transfer efficiency is reduced; it can be directly used for materials with suspended solids easy polymerization; it is suitable for complex distillation such as side feed discharge, etc. There are many types of tower equipment. Tower equipment is one of the most important equipment in chemical, petrochemical refining production. It can make gas-liquid liquid-liquid two-phase contact closely achieve the purpose of mass transfer heat transfer between phases. Common unit operations that can be completed in tower equipment include distillation, absorption, desorption, extraction, etc.