The ideal packing should provide suitable channels for gas phase and liquid phase, and the pressure of gas flow will be reduced, the flux will be large, the liquid flow will spread easily into a liquid film, and the surface of the liquid film will be updated quickly. In addition, the requirements of convenient manufacture, low price, certain strength, heat resistance and corrosion resistance, and good wettability to surface materials and liquids should also be considered.
Commonly used fillers include bulk fillers and structured fillers. The former can be piled in the tower or built as a whole. Common packaging is as follows:
1, Lassie ring, this is a short tube with the same height and outer diameter, which can be made of ceramics and metals. Raschig ring is widely used because of its simple shape, easy manufacture and clear characteristics in fluid mechanics and mass transfer. However, due to its large height-diameter ratio, it is easy to form line contact between adjacent rings during stacking, and the uniformity of packing layer is poor. Therefore, there is a serious wall flow in the liquid in the packing layer of Lassie Ring.
2. Bauer ring is developed on the basis of Lassie ring. It punches one or two layers of rectangular holes in the circumferential direction on the wall of Lassie ring, but the base material of the hole does not leave the ring, but bends inward to the center of the ring. This structure improves the effective utilization of the inner space and inner surface of the ring and greatly reduces the airflow resistance, so it is especially suitable for vacuum operation. The two layers of square holes on Bauer ring are staggered, even if they are adjacent when accumulating.
3. The rectangular saddle-shaped packing has asymmetric packing structure, different sizes on both sides of the packing, so that the packing layers will not overlap during stacking, the uniformity of the packing layers is greatly improved, the gas flow resistance is small, the handling capacity is large, and the manufacturing is convenient.
4. Trapezoidal ring packing, similar in structure to Bauer ring, with rectangular holes in the ring wall and two layers of crossed fins staggered at 45 degrees in the ring. The height of the ladder ring is usually only half the diameter, and one end of the ladder ring is made into a bell mouth. Therefore, in the packing layer, the packing contacts at multiple points, the bed layer is uniform and porous, the gas flow resistance is reduced, and the production capacity is high.
5. Mesh packing made of metal mesh or porous metal sheet is commonly known as mesh packing. It is characterized by fine mesh, small packing volume, large specific surface area and porosity, and strong liquid uniform distribution ability. Therefore, the gas resistance of mesh packing is small and the mass transfer efficiency is high, but its manufacturing price is relatively high.