4 replies to this topic

[EMachado]

Hello, i would like to calculate the efficiency of the mole sieves i have in the plant where i work, i've been trying to do this in Hysys but it seems that there is no built-in operation in order to do this, if someone have done this task before i'll be glad to know. The process has to towers, while one tower is adsorbing the other one is regenerating, and the main purpose of this is to take out the humidity from a propane/propylene liquid mixture.

Thanks.

[Zauberberg]

It cannot be done in Hysys - at least not in the way you described. Adsorption on Molecular Sieves is dynamic process depending on several parameters and, as such, it is not available within Hysys' unit operations.

On the other hand, why to use software for that? I believe you want to calculate how many kilograms of moisture is adsorbed from the feed stream on 100kg of Mol Sieve and compare it against design figures. You can easily do that by analyzing feed stream for moisture content and calculating material balance around the adsorbers during active (adsorption) cycle.

If you are looking for something else, let us know and we may assist you further.

[EMachado]

Hello Zauberberg, thanks for your answer. Yes, you're right, i'll try with that one. Is there any other way to estimate how much humidity i can take out of the mixture (dependent variable) for a given inlet humidity for the inlet stream (independent variable)?, with a fixed geometry, temperatures, pressures and times cycles of adsorbing/regeneration, as you can see this is an existing unit, it's not a new design. I need this calculation to decide if its desirable to change the zeolite of the towers.

By the way, do you know any resource (book, paper, calculation method) to estimate the performance of this kind of units?. I have my unit operations bibliography but it would be better to check how others have done it, as well as other calculation methods.

Thanks.

[Zauberberg]

Again, moisture adsorption capacity depends on many factors. Even for the same type and quantity of desiccant, two systems may perform differently due to e.g. channeling that could be a consequence of desiccant damage in one of the cases/systems. For the original designs, my recommendation is to get in touch with the adsorbent vendor and you can obtain a lot of information required for your work.

As for the literature - look for GPSA Databook and JM Campbell "Gas Conditioning and Processing". They offer quite nice description of the process, including design procedures for adsorption and regeneration.

[ankur2061]

Mole Sieve dehydration units are well described in GPSA Engg Databook, in the subsection titled Solid Desssicant Dehydration (Section 20: Dehydration). The subsection provides guidelines for determining mole sieve bed size (bed diameter and bed length) as well as regeneration calculations in terms of heat supplied to the bed to desorb water from the saturated bed.

Another authoritative source for mole sieve design and evaluation is the book "Funadamentals of Natural Gas Processing" by Arthur J. Kidnay and William R. Parish (Chapter 6 -Gas Dehydration, Section 6.3.2 - Adsorption Processes)

Regards,
Ankur.