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[Leronira]

Here's a simple question.
How does the loading and flooding points changes when a structured packing is used instead of random packing.

Here's what I've come up with. But I know the answer is wrong.

If a random packing is use, there will be higher pressure drop in the vapor phase. Higher pressure drop means the vapor will be at a lower pressure as is flows up the column. This results in a lower resistance acting on the water that is flowing down the column, hence lesser chance of loading/flooding.

However, the correct answer should be, in a structured packing, the loading and flooding occurs at a higher gas mass velocity.

Can anyone guide me and explain to me why is this so?
Thanks a lot in advance

Edited by Leronira, 23 December 2010 - 12:23 AM.

[Zauberberg]

Leronira,

It isn't that much complicated, at least per my understanding. When looking at any type of packing, there is an inverse relationship between capacity and mass transfer efficiency - higher capacity equals to lower efficiency (higher HETP), and vice versa, for the same tower diameter and packing height.

Applied to two different sizes of random packing, obviously the packing that is smaller in size will have higher efficiency but it will begin to flood before the packing larger in size will start to flood. This is because the smaller packing will have higher liquid holdup due to higher pressure drop of upflowing vapors, and this is again the consequence of smaller open area of smaller-size packing, as compared to larger-size packing. The higher the liquid holdup is, the system is closer to the flooding point.

If you want to compare two different types of packing (random vs. packed), you must specify exactly what type/size of packing is in question, and what are their performance parameters for given application. For example, a grid-type structured packing will definitely have higher capacity (and higher flooding point) than many types/sizes of random packing, while on the other hand, a high-efficiency structured packing is going to flood much before any of the random packed towers.

http://www.koch-glit...ibrary/KGSP.pdf
http://www.koch-glit...rary/KGIMTP.pdf