Plate height of filler, etc

The plate equivalent height of the packing is generally related to factors such as the F-factor of the system; a higher F-factor results in a greater plate equivalent height. The technical parameters for packing regarding plate equivalent height should fall within a certain range rather than being a fixed value.

This post was last edited by brainandrain on 2009-5-3 at 19:32. 1 Structural properties of fillers: These are generally related to the specific surface area and porosity, with different fillers showing differences that can range from several times to dozens of times. 2 Unit operation process: The HETP for distillation is lower than that for absorption and stripping processes; for isomers, the HETP is generally lower than that for the separation of other substances. 3 Tower operation conditions: Such as whether the reflux is sufficient to wet the packing, whether it is at the edge of flooding, etc., as well as the end effects of tower operation and the distribution efficiency of the distributor. 4 Different filler manufacturers may vary in their approaches; large, reputable filler producers will use standard tests to determine the mass transfer and hydraulic properties of their fillers. For structured fillers, the F factor is generally used as an indicator of their mass transfer performance, while for randomly arranged fillers, the flooding rate needs to be taken into consideration. In vacuum conditions, the pressure drop across the filler also needs to be considered when selecting a filler. 5 For process designers, it is generally sufficient to provide the number of theoretical plates and recommend the appropriate packing as well as its height; for engineering design, it is advisable to have the cooperation of packing manufacturers.

The theoretical number of theoretical plates is not the same as the actual number of plates; it is determined based on various parameters such as the operating gas velocity of the tower, plate efficiency, packing height, and plate spacing, and is not designed solely through theoretical calculations.

If the calculated theoretical number of theoretical plates for a certain packing is 20, and 40 plates are required to separate a particular product (with 100% column efficiency), then 2-meter packing should be chosen. This is correct.

The equivalent plate height of a certain packing is based on experimental data under specific conditions; in engineering design, it is necessary to select an appropriate value taking into account various factors such as the type of gas-liquid distributor, among other issues related to the components inside the tower. Theoretically, the number of theoretical plates is 20, while 40 plates are required to separate a particular product (with 100% tower efficiency). Choosing 2 meters of packing can be understood in this context.

The original poster’s understanding is correct; 2 meters is sufficient.

Imagine that within a packed tower, the packing layer is divided into several equal height segments; each segment functions as one theoretical plate. The height of such a segment is referred to as the theoretical plate equivalent height, or equivalent plate height, denoted by HETP. The height of the packing layer is obtained by multiplying the number of theoretical plates by the plate height. In the owner’s example, HETP=1/20=0.05m; therefore, the required packing height is 0.05*40=2m. Is this explanation clear to the owner now? This post was last edited by ljfwp on 2009-4-4 16:49.]

May I ask what the theoretical number of plates for a screen corrugated packing is?

In practice, a margin must definitely be reserved, as the operating pressure has a significant impact on the number of theoretical plates. The tower diameter does have an impact, but it can be improved through careful design, manufacturing, and installation processes. Experiments have shown that under optimal operating conditions, the tower diameter has no effect on the number of theoretical plates. Given that the number of theoretical plates for the packing used in this case is so high, the tower diameter will not be very large; therefore, the impact of the tower diameter is relatively small.

This issue cannot be generalized; generally, the determination of the theoretical number of plates for packing is carried out under ideal conditions, and as a rule this value tends to be on the high side. Therefore, when selecting the height of the packing, it’s advisable to leave some margin. The theoretical number of plates is closely related to the kinetic energy factor of the gas phase. When choosing packing, the kinetic energy factor should not be set too high – for example, for random-packed packing, it should not exceed 0.5, and for metal mesh packing of type 700Y, it should not exceed 1.0. Although the operating kinetic energy factor for 700Y ranges from 1.7 to 2.4, it still shouldn’t be set too high, in order to allow for operational flexibility. This is just my humble opinion; I’m not sure if it’s correct, but it’s provided for reference only

The plate height is the height of the packing that should be capable of achieving the separation effect of one theoretical plate. Numerically, it is equal to the reciprocal of “the number of theoretical plates per meter of packing”. //For example, if the product specifications for a certain type of packing state that there are 20 theoretical plates per meter of plate length, and if separating a certain product requires 40 plates (with 100% tower efficiency), should one then use 2-meter-long packing? // I understand it the same way.

The original poster is incorrect; the equivalent plate height of this packing, as described in the packing specifications, is determined based on certain specific operating conditions. Generally, it refers to the calculated height in a distillation column. Because among various calculations, the accuracy of calculations for distillation columns is the highest. Relatively speaking, the results calculated for processes such as absorption and mass transfer differ significantly from the actual values. Therefore, it is quite risky to take this best result to general settings. Therefore, I believe that the product specifications for a certain type of packing state that the theoretical number of theoretical plates per meter of plate is 20. If separating a certain product requires 40 plates (with a tower efficiency of 100%), then using only 2 plates is far from sufficient. It depends on the specific process involved, as different processes require different numbers of plates; however, it should be at least more than 2 plates.

Operability of the tower: When choosing the height, be sure not to forget to leave some room for operational flexibility in the tower. For example, a packing height of two meters is sufficient, but in actual design, it is necessary to add 100–200 millimeters of flexibility to that two-meter height. Because we all know that in practice, the actual processing capacity of a tower is slightly higher than its designed capacity. These are my personal opinions; I’m not sure if they will be helpful for the original poster’s design. If there’s anything wrong in what I’ve said, I hope everyone can offer some guidance

I can’t select the packing plate; how can I switch to choosing a plate tower? How to do this? I seek advice from experts.