Working principle of packed tower
Packed tower is one of the most important equipments in chemical industry, petrochemical industry and oil refining.
First, let's understand the structural characteristics of the packed tower:
Packing tower is a kind of mass transfer equipment which uses the packing in the tower as the contact component between gas and liquid. The body of the packed tower is a vertical cylinder, and the bottom is equipped with a packing support plate. The packing is placed on the support plate in a disorderly or integral way. A packing pressing plate is installed above the packing to prevent it from being blown by the rising air flow. Liquid is sprayed on the packing from the top of the tower through the liquid distributor and flows down the packing surface. The gas is sent from the bottom of the tower and 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 and 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 and 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 and redistributed in the middle. The liquid redistributor consists of liquid collector and liquid redistributor. The liquid flowing from the upper packing is collected by the liquid collector and 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 and large operation flexibility.
The packing tower also has some shortcomings, such as high packing cost; when the liquid load is small, it can not effectively wet the packing surface, so that the mass transfer efficiency is reduced; it can not be directly used for materials with suspended solids or easy polymerization; it is not suitable for complex distillation such as side feed and discharge, etc.
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