1 reply to this topic

[iren]

Dear all,

I'm a project engineer working for a small industrial gas company. Our ASU is about 20 years old and the adsorber material used for air drying and purification before distillation has never been changed so far. During the last summer periods we had problems with CO2 breakthrough and reduced the production air volume as a consequence. Next year we need to change the adsorber beds but since higher performing material is available we'd like to evaluate whether a change of product could bring us some efficiency in the process.

Is there anyone out there who did something similar before?
Is it worthwile changing the typ of molecular sieve to prolong adsorption time?
What are the consequences on heating and cooling time for regeneration?
Do I need to recalculate the bed size of alumnia?
Do I safe some energy at all, if I change for a higher performing molecular sieve?

I can give you information about the products and the process parameters, if this is of any help.

Thank you and best regards,
iren

[Art Montemayor]

Iren:

I have worked with adsorbents since the introduction of Molecular Sieves by American Linde (div of Union Carbide) in 1960, when they won engineering acclaims for the discovery of synthetic, tailor-made adsorbents. I was among the first in my company to introduce fixed bed adsorbent systems as dual CO2 and water removal units prior to Air Separation Plants. I believe I have the credentials to tell you that if you have used the same mol sieve bed on the same air separation column for the last 25 years without changing out the adsorbent, then you have severly abused the expected performance of the adsorbent. Any experienced process engineer with operating experience in L'air liqude will tell you the same. A reasonable, well-designed bed should last no longer than 24,000 to 40,000 hours - approximately 3 to 5 years.

The fact that you claim 20 years of life with the same bed is outstanding and incredible. You may have operated a grossly over-designed bed, but bed poisoning, aging, and attrition will always have occurred. I don't see any reason why you should want to try a "better" mol sieve. I think you've already found the best mol sieve.

There is an old Texas saying: "If it ain't broke, don't try to fix it." I believe it applies to your case. You say higher performing material is available, but I challenge anyone to improve on the 20-year record you claim. Go directly to the major adsorbent manufacturers in the world and they probably will tell you the same thing. If they can guarantee you a life better than 20 years, come back and tell us all about it. I personally don't think you will find any performance to beat what you have already attained. Granted, I don't know your superficial velocity, your design sorptivity figures, your type of regeneration and regen temperatures, as well as all the process design data. But nevertheless, 20 years has to be among the best adsorbent lives ever achieved by anyone in air separation service.

I would always work directly with your preferred adsorbent supplier and rely on their recommendations and experience. When you use a world-class adsorbent manufacturer, you will always obtain excellent engineering service and advice on what adsorbent to use and how to use it. That is your best and most reliable source of know-how - not an engineering Forum. I have had a lot of experience with adsorption beds; but American Linde has had exponentially even more experience and they are the type of supplier that can best help and advise you.

Congratulations on your excellent adsorbent performance life. It would be a blessing to all who read this thread to read about your design and operating parameters with this unit over the past 20 years. I know I would be very grateful on knowing how you achieved this performance.