Hello everyone, regarding distillation: should a plate tower or a packed tower be used?

Theoretically, both plate towers and packed towers can be used in distillation; each has its advantages and disadvantages. Since I don’t know the process parameters, I’m unable to advise which type of tower would be better in this case. There is a company here called Tianjin Xinxing Tower Equipment Technology Development Co., Ltd.; this company is pretty good

Typically, small towers use packing, while large towers use plate towers.

There’s no fixed rule for this. As mentioned above, packing is usually chosen for small towers, while plate-type designs are preferred for larger towers. Additionally, a plate-type design can be opted for in new projects, which facilitates future expansion and upgrades. Since packed towers tend to have smaller height and diameter compared to plate towers, packed towers can be considered when space is limited in the installation ； Since trays are cheaper than packing, the investment cost for plate towers is usually lower than that for towers using packing. The specific form to choose depends on the actual conditions of the device.

What liquid-to-vapor ratio is suitable for a packed tower?

It must not be too large nor too small to be used in a packed tower

There isn’t really any essential difference between the two types of towers, right? The tray type is more traditional, with well-developed methods for calculation and simulation; of course, the increasing use of the packed-bed type also indicates that its calculation and simulation techniques have become mature as well. Many universities do a good job in areas such as the design calculations for distillation columns and tray design, including Tsinghua University and Hebei University of Technology.

Comparison between plate towers and packed towers: For many counter-current contact processes, both packed towers and plate towers can be used. Different tower types have their own advantages and disadvantages, and a choice should be made based on a comprehensive consideration of the process system. ⑴ The operating range of a packed tower is limited, and it is particularly sensitive to changes in the liquid load. ⑵ Packed towers are not suitable for treating materials that are prone to polymerization or contain solid suspensions. ⑶ Packed towers are not suitable when cooling is required during the gas-liquid contact process to remove reaction heat or heat of solution. Furthermore, when there is a side-line discharge, packed towers are also less convenient than plate towers. ⑷ The diameter of a packed tower can be quite small, but the diameter of a plate tower is generally not less than 0.6 m. ⑸ Design data for plate towers is more readily available and more reliable, allowing for smaller safety factors. ⑹ When the tower diameter is not very large, the cost of a packed tower is low.

Comparison between packed towers and tray towers 1) Comparison of hydrodynamic conditions Tray tower: Stepwise contact, mass transfer occurs on the tray surfaces. Bubble flow: Gas: dispersed; liquid: continuous. Jet flow: Gas: continuous; liquid: dispersed. Mixed flow: A transitional state. Packed tower: Continuous contact, mass transfer occurs on the surface of the packing. Usually: Gas: continuous; liquid: flows in a film-like manner. With large liquid volumes: Mixed flow state, with strong interaction between gas and liquid phases. With small gas volumes: Bubble flow, with the liquid filling the packing. 2) Comparison of pressure drops Pressure drop, Pa/theoretical stage: Floating valve tower – 400–1500; MD tower – 300–1500; 50# Pall ring – 80–400; 250Y packing – 30–150. 3) Selection of tower type △Vacuum distillation: Increases volatility and lowers boiling points (for substances with high boiling points or that are heat-sensitive), resulting in energy savings. Regularly packed towers should be preferred. Reasons: a) Lower pressure drop (about 1/5 that of floating valve towers). b) Higher throughput (40–100% higher than that of tray towers). c) Higher efficiency (better use of space and larger mass transfer area). △Pressurized distillation: Gas phase: High density, low flow rate； Liquid phase: Low density, high flow rate – plate towers should be preferred. a Pressure drop is not a major issue. b The efficiency of packed towers decreases, while that of plate towers increases slightly. c The flux in packed towers declines. a Gas-phase backmixing: High density of the gas phase, low density of the liquid phase. b High liquid-phase flow rate: Leads to uneven flow. c High liquid-phase flow rate: Results in an thicker liquid film, increased resistance, and reduced efficiency. △In actual design, all factors must be taken into consideration: a Equipment investment, b Operating costs, c Ease of maintenance

It is generally determined based on operating conditions, material properties, utility conditions, etc.

Packed towers and plate towers each have their advantages; it’s hard to say which is better. Generally speaking, distillation focuses on sharing efficiency; the advantages of this packed tower are quite evident, but some materials are not suitable for use with packing……

For those with a small diameter, a packed tower is more economical.

Generally, it is more economical to use packing for towers with small diameters, while tray plates are used for towers with large diameters； However, when the pressure is low and the gas-liquid load is high, it is more reasonable to use packing ； When a lower pressure drop within the tower is required, the pressure drop across the packing is also reduced ； Packing is preferable for low-pressure operations, while plate towers should be used for high-pressure operations.

What is greatness? What is small? Packed towers can now be used in towers with a diameter of over 16 meters. As for towers with smaller diameters, such as DN200 and below, loose-packed packing is likely to be used more frequently (although structured packing is also used; our company has towers of this type).

Now, the large tower can also use a packed tower!

It is rare to hear that utility conditions can determine the type of internals in a tower. Could you explain why?

Judging from the current situation, fillers can also be used in large towers; the tower at our factory has a diameter of 3400, and fillers are used there as well, with decent results. I think for distillation design, one should turn to Tianjin University. They have design experience with several large companies, and those designs have been successfully put into use, including those for our factory as well. They have their own pilot plant facilities, and more importantly, they possess a wealth of data from large-scale production tests. You might as well give them a call and ask.

Universities have many departments, and there are even more units that work together.

Compared with plate towers, packed towers not only have a simpler structure, but also feature high production capacity, high separation efficiency, low liquid holdup, great operational flexibility, and reduced pressure. However, packed towers are expensive; they are not suitable for liquid streams containing suspended solids or systems that tend to polymerize, and they are also not very appropriate for applications with side outlets.

Is there any misunderstanding? What I meant is the gas-liquid ratio, not the tower diameter; obviously, a smaller tower diameter is advantageous for packed towers.