A packed tower is a gas-liquid mass transfer device that uses a large amount of packing material as the interphase contact component. Packed towers were applied to industrial production in the mid-19th century, and subsequently, they and plate towers developed in close competition, forming two distinct types of gas-liquid mass transfer devices.
The tower body of a packed tower is a vertical cylinder with a support plate at the bottom. The packing material is placed on the support plate in a random or modular manner. A packing pressure plate is installed above the packing to restrict its movement with the rising gas flow. Liquid is added from the top of the tower, sprayed onto the packing through a liquid distributor, and flows down the surface of the packing. Gas is introduced from the bottom of the tower, distributed by a gas distribution device (small-diameter towers generally do not have a gas distribution device), and flows countercurrently with the liquid through the voids of the packing layer. Mass transfer occurs through close contact between the gas and liquid phases on the packing surface. Packed towers are continuous contact gas-liquid mass transfer devices; the composition of the two phases changes continuously along the tower height. Under normal operating conditions, the gas phase is the continuous phase, and the liquid phase is the dispersed phase.
As liquid flows down the packing layer, it tends to concentrate towards the tower wall, causing a gradual increase in liquid flow near the wall. This phenomenon is called wall flow. The wall flow effect results in uneven distribution of the gas and liquid phases within the packing layer, thus reducing mass transfer efficiency. Therefore, when the packing layer is high, it needs to be segmented, with a redistribution device installed in between. The liquid redistribution device consists of a liquid collector and a liquid redistributor. Liquid flowing down from the upper packing layer is collected by the liquid collector and sent to the liquid redistributor, where it is redistributed and sprayed onto the upper packing layer.
The packing is the core component of a packed tower, providing the phase interface for gas-liquid mass transfer and being a major factor determining the performance of the packed tower. There are many types of packing, which can be divided into two main categories based on the packing method: bulk packing and structured packing.
