December 2, 2010 (One Question per Day)

(1) A packed tower should be selected when low pressure is required. Because the free cross-sectional area of a packed tower is generally greater than 50%. Gas resistance is low. When handling heat-sensitive materials that are prone to decomposition or polymerization at high temperatures, operating under vacuum can lower the temperature at the bottom of the tower; a packed tower is therefore very suitable for this purpose. 2 V. B! k; z0 S% t; \9 J+ P# ~ (2) Materials that are prone to foaming can cause flooding in plate towers, whereas packing can usually break down these bubbles. (3) When handling corrosive materials, a packed tower is more advantageous, as there are a wide range of materials that can be used for the packing – non-metallic materials such as ceramics and plastics can be employed; they are both inexpensive and effective. The materials for the trays in plate towers are generally metals, leaving little room for choice. (4) When the mass transfer rate is controlled by the gas film, a packed tower is selected. Since the surface of the packing is covered by a thin liquid film, gas-phase turbulence helps to reduce the resistance caused by this liquid film. On the contrary, when the mass transfer rate is controlled by the liquid film, a plate tower can be used, as it allows for turbulence in the liquid phase to be maintained on the tower plates. (5) The diameter of the tower is less than 800 mm. It is generally advisable to use a packed tower. Such as using a plate tower. Then it will be difficult to fix and seal the tray. Currently, due to the development of new types of packing, especially structured packing, large-diameter packing towers are also widely used. Among them, the diameter of the corrugated packed tower has exceeded 14 meters

1. High operational flexibility 2. Self-cleaning capability 3. Long vapor-liquid exchange time 4. Easy maintenance

1 Reduce tower height 2 High load 3 Low pressure drop 4 High separation efficiency 5 Energy saving

Under normal operating conditions, the pressure drop in a packed tower is definitely lower than that in a plate tower; this is why packed towers are often chosen for vacuum towers, as these towers have stringent requirements regarding pressure drop. The notion of gas resistance is incorrect. Generally speaking, at low pressures and in vacuum conditions, packed towers perform better in terms of gas-liquid contact and mass transfer compared to plate towers. However, at high pressures, as the difference in density between gas and liquid decreases, the use of packing leads to an increase in the thickness of the liquid film on the surface, which hinders surface renewal and mass transfer. Therefore, plate towers are usually preferred in such cases. The factors mentioned above are just some of the considerations involved in choosing a tower type in engineering; other factors include the properties of the material and the application scenario, as well as past engineering experience