Packed tower is a mass transfer device in which the packing in the tower is used as the contact member between the gas and liquid phases .
The tower body of the packed tower is a vertical cylinder, and the bottom is equipped with a packing support plate , and the packing is placed on the support plate in a random stacking or whole building manner.
A packing pressure plate is installed above the packing to prevent it from being blown by the updraft.
sprayed onto the packing from the top of the tower through the liquid distributor , and flows down along the surface of the packing.
The gas is fed from the bottom of the tower, and after being distributed by the gas distribution device (generally, there is no gas distribution device for small diameter towers), it continuously passes through the gap of the packing layer in countercurrent to the liquid. On the surface of the packing, the gas and liquid phases are in close contact 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 operating conditions, the gas phase is the continuous phase and the liquid phase is the dispersed phase.
When the liquid flows down along the packing layer, there is a tendency to gradually concentrate to the tower wall, which makes the liquid flow near the tower wall gradually increase, which is called wall flow.
The wall flow effect causes uneven distribution of the gas-liquid two phases in the packing layer, thereby reducing the mass transfer efficiency.
Therefore, when the packing layer is high, it needs to be segmented, and a redistribution device is arranged in the middle.
The liquid redistribution device includes two parts: a liquid collector and a liquid redistributor. The liquid flowing down from the upper packing is collected by the liquid collector, and then sent to the liquid redistributor. After redistribution, it is sprayed onto the lower packing.
Packed towers have the advantages of large production capacity, high separation efficiency, small pressure drop, small liquid holdup, and large operating flexibility.
Packed towers also have some shortcomings, such as high cost of packing; when the liquid load is small, the surface of the packing cannot be effectively wetted, which reduces the mass transfer efficiency; it cannot be directly used for materials with suspended solids or easily polymerized; Complex rectification such as discharge is not suitable.
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