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Molecular sieves in gas processing: Effects and consequences by contaminants

01.01.2013  |  Terrigeol, A. ,  CECA SA, Paris, France

The principles of adsorption on molecular sieves are easy to understand, but practice sometimes reveals traps to avoid.

Keywords: [sieves] [gas processing] [zeolite] [acid gas] [sulfur] [mercury] [removal] [adsorption] [molecules]

In the natural gas processing chain, pretreatment typically includes removing acid gas, sulfur and mercury. The moisture specification of the gas depends on the downstream equipment. When cryogenic processes are involved, such as in natural gas liquids (NGLs) recovery or liquefied natural gas (LNG) production, avoiding hydrates requires water dew points that only zeolite-based molecular sieves can achieve.

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I'm a student in chemical engineering in master course and i want to do conceptual design for dehydration unit with molecular sieve adsorbents and i don't know what should i do?
could you introduce me some references about that.
thank you

Alexandre Terrigeol

Dear Youcef,
Thank you for your comment and question. Yes, the smaller the particles, the larger the surface area directly accessible to the fluid, and therefore the shorter the MTZ. So if your adsorption is downflow, the layout seems correct to me.

Alexandre Terrigeol

Dear Faranoush,

Thanks for your comment. Actually the regeneration is not always provided by the product gas and several possibilities exist. However, I would rather say that the heavy HC that may participate to coking with time are more related to the feed (or entrained, or due to retrocondensation,...).

faranoush ahmadi

Dear Mr. Terrigeol,

It seems that heavy hydrocarbons may cause coking during regen of mole sieve beds so why regen gas is normaly provided from dehydrated gas but there is no design for getting regen gas from downstream units for example overhead of de-C1 or de-C2? is there any concern for molecular weight? is it only cost issues for not using lean gas?
Thanks for your respond in advance


I am project manager of gas treatment plant in south desert -Algeria.
We actually carrying out the ceramic ball and Catalyst filling work for dehydrators.
The activated Alumina is filled as follows:
1. lowest bed: AA 1/16'' (smaller): bed height 900 mm
2. highest bed: AA 1/8'' (bigger) : bed height 5 500 mm
We follow theUOP procedure, my question is
Is it the best design based on your principles, the smaller diameter should be installed in teh MTZ ?
''The larger the accessible surface, the shorter the MTZ. To optimize the surface area and therefore the global bed length, most designs involve smaller particles in the MTZ compared to the EZ''.

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