Problems with distillation towers

A plate tower operates on a stepped process, while a packed tower is a continuous process! ! ! !

For many counter-current gas-liquid contact processes, both packed towers and plate towers can be used; the designer must choose one based on the specific circumstances. There are many differences between packed towers and plate towers, and understanding these differences is helpful for selecting tower equipment appropriately. Comparison between packed towers and plate towers: 1. A packed tower is a continuous gas-liquid mass transfer device, where the gas and liquid phases are in continuous counter-current contact for mass and heat transfer; the concentrations of the components in these two phases change continuously as one moves upward within the tower. 2. In a plate tower, the gas and liquid phases come into counter-current contact layer by layer, allowing for mass and heat transfer; the concentrations of the components in the gas and liquid phases change in a stepwise manner along the height of the tower. Advantages and disadvantages of packed towers: ① Packed towers have a limited operating range, and they are particularly sensitive to changes in liquid load. When the liquid load is low, the filler surface cannot be properly wetted, resulting in a sharp decline in mass transfer efficiency ； When the liquid load is too high, flooding is likely to occur. Well-designed plate towers have a much larger operating range. ② Packed towers are not suitable for handling materials that are prone to polymerization or contain solid suspensions, whereas certain types of plate towers (such as large-pore sieve plates and bubble columns) can effectively handle such materials. Furthermore, cleaning a plate tower is also easier than cleaning a packed tower. ③ When cooling is required during the gas-liquid contact process to remove reaction heat or heat of solution, packed towers become structurally complex due to the issue of liquid distribution. Plate towers allow cooling coils to be installed on the trays easily. Similarly, when there is a side-line discharge, packed towers are less convenient than plate towers. ④ In the past, the diameter of packed towers was rarely greater than 0.5 m; later on, it was considered that it should not exceed 1.5 m. However, given the development of packed towers over the past 10 years, this limitation no longer seems to hold true. The diameter of a plate tower is generally not less than 0.6 m. ⑤ Design data for plate towers are more readily available and reliable, therefore the design of plate towers is more accurate, allowing for a smaller safety factor. ⑥ When the tower diameter is not very large, the packed tower is inexpensive due to its simple structure. For systems prone to foaming, the packed tower is more suitable, as the packing helps to limit and break down foam. ⑧ For corrosive media, packed towers are more suitable, as ceramic packing can be used. ⑨ For thermosensitive systems, packed towers are preferable, as the liquid holdup in packed towers is lower than that in tray towers, resulting in a shorter residence time of the material within the tower. ⑩ The pressure drop of the tower is lower than that of a plate tower, making it more suitable for vacuum operation.

Comparison of plate towers and packed towers: Plate tower, Packed tower. Pressure drop: Higher, Smaller; Packed materials: Larger in size； Larger-sized packing and structured packing result in a higher empty tower gas velocity, while smaller-sized packing leads to a lower one ； Large-sized packing and structured packing result in a more stable tower efficiency as well as higher efficiency; traditional packing yields lower efficiency ； New type: random packing and structured packing; high liquid holding capacity; larger/lower; liquid-to-gas ratio; wide range of applicability; certain requirements regarding liquid volume; easier/more difficult to install and maintain; material: common metal materials; both metal and non-metal materials can be used; cost: lower for larger diameters; higher investment for new type of packing

Thank you for the reply from the third floor; it was very comprehensive. Great job! :handshake

The choice between plate towers and packed towers depends mainly on the characteristics of the installation and the specific process requirements. Domestic technology in this area is already quite advanced; generally, plate towers are used in the oil refining industry, while packed towers are preferred in the chemical industry.