8 replies to this topic

[YiingShian]

Hi, i would like to know how to calculate the height of adsorbent required to adsorb water vapor and carbon dioxide from my system. I am currently designing a desiccant dryer with an inlet temperature of 14 DegC, 100% RH, 8 bar air. The adsorption time would be 4 hours, activated alumina would be use to adsorb water vapor while Zeolite 13X would be use to adsorb carbon dioxide. The target amount of water vapor removed is 33867 Kg and  for carbon dioxide on the other hand is 4846 kg. How do i determine the height of the bed required for both activated alumina and zeolite 13X. Aside from this does these amount of desiccant sounds too much and do i have to use multiple desiccant dryer to accommodate this?

 

kg h20/ kg Activated Alumina 1.78E-02   Amount of Activated alumina req 1902637.51 Kg kg CO2/ Kg Zeolite 13x 0.237654   Amount of Zeolite 13x req 20390.00344 Kg

 

[Bobby Strain]

You usually get quotes for such systems. And the vendor will size the beds. Congratulations. You are the first that I have seen spell desiccant properly in a long time. Your numbers seem too precise for engineering.

 

Bobby

[breizh]

hi ,

 Consider reading the attachment , you will find pointers .

 Please round your numbers and make sure what you wrote is understandable ( last sentence) .

Good luck.

 

 

Breizh

Edited by breizh, 12 November 2018 - 05:08 AM.

[Bodhisatya]

Hello

 

Sounds like you are referring to Pre Purification units used in Air Separation plants. You need to know the dynamic adsorption capacity of each desiccant, to quantify the amount of adsorbents, which finally will give u height of the BED.  The overall height of the Adsorbent tower will depend if you are using in-built after filters inside PPU or not.  BTW is it a vertical tower or a radial one.

 

To uncomplicate the matter, give me the air flow in base condition or flowing conditions, as well as desired outlet conditions in ppm of CO2 and water, Can come back to you with a figure, though actual numbers might vary a bit vendor wise.

 

Bodhisatya.

[Art Montemayor]

yslim1997:

 

I don’t know if you are a student or a practicing, graduate engineer.  I started operating and eventually designing and building some of my own adsorption units when I was a young engineer, over 58 years ago.  I will assume license to make some comments on your post as follows.

• Please refer to the attached, which are a few of the many papers I have on adsorption.  You will find answers to what I believe are your specific questions in the edited and formatted copies that I have prepared of some engineering conferences I have been to in the past.
• Calculating the height of an adsorption bed is rather simple and I question why you need to make the calculation if you are not familiar or experienced in an adsorption Unit Operation.  Your queries indicate that you are not familiar with adsorption.
• If I am correct, why are you attempting to calculate what is probably a required unit?  As Bobby Strain has indicated, this is normally left to a recognized adsorption designer and fabricator company.  50MMScfd of compressed air is a relatively large unit and if you don’t have the experience, I would advise you to purchase the design rather than try to design it yourself.  8 bars (120 psig) is a relatively low pressure to employ in an adsorption unit.  What, specifically, are you doing this for?  Is this atmospheric air?
• I will not calculate the information needed to answer your questions.  Our experienced Forum members will all probably state the same since we normally would charge for such service and no one would assume the responsibility for the results obtained when the design is applied using the free, estimated information.
• You don’t specify if you are using a TSA or PSA regeneration (Thermal or Pressure Swing Adsorption) system.  Which one is it?
• You also don’t state how many towers you are using.
• You want to use Activated Alumina for removing water and Mol Sieves for removing CO₂.  Are these two adsorbents to be used in the same adsorber vessel, one bed on top of the other?  Are you aware that these two types of adsorbents have very different temperature requirements during regeneration (in case you are using TSA)?  You should supply a detailed sketch of the tower arrangements together with the flow arrangements for adsorption and regeneration in order for our members to know specifically what kind of adsorption system you are implementing.  There are many variations of how an adsorption system can be designed and arranged - 2 tower, 3 tower, open, closed, etc., etc.
• The attachment paper that Breizh supplys is not applicable to adsorbents.  It is meant for calcium chloride deliquescent tablets used in dehydrating natural gas.  That is why I am attaching some applicable papers to this post.
• I get the impression that you are a student when I see your following statements:

"kg h20/ kg Activated Alumina 1.78E-02
Amount of Activated alumina req 1902637.51 Kg
kg CO2/ Kg Zeolite 13x 0.237654
Amount of Zeolite 13x req 20390.00344 Kg"

• Practicing engineers would never cite the amount of alumina needed to the hundreth decimal place.  That is naiveté.

We can furnish you with our comments and recommendations if you supply your detailed calculations and drawings.  With scarce basic data, all that can be offered is our general comments and ideas.

 

​  Recent Developments in the Application of Molecular Sieves - 1958.docx   994.85KB   37 downloads

 Gas Dehydration by Adsorption - 1952.docx   309.08KB   36 downloads

 Dehydration With Molecular Sieves - 2004.docx   1.61MB   45 downloads

 Fundamentals of Adsorptive Dehydration 2004.docx   846.67KB   50 downloads

[YiingShian]

Bodhisatya:

 

Hi sorry for the late reply, the conditions are as follow, inlet is at 14 degreeC, 8 bar and 100% RH

Attached Files

•  Capture.PNG   16.83KB   4 downloads

[YiingShian]

Art Montemayor:

 

HI

 

I'm currently an engineering student.  I am currently on a project on cryo liquid air energy storage plant.  I had to design the air purification systems to clean incoming air off carbon dioxide and water vapor to prevent damage to downstream liquefaction processes.  I am planing to use a TSA due to the large flow rate, an externally heated blower type desiccant dryer in exact.  I am trying to calculate for 1 unit first before deciding on how much unit to split into.  I figure 8 bar is quite enough after referring to an Atlas Copco desiccant dryer brochure.  May I know what is the typical pressure used in the industry?   I plan to place both adsorbent in the same tower, where Activated alumina comes first followed by zeolite 13x.  May I know if it is possible to regenerate both of them at the same regeneration temperature which i am now assume to be 290 deg C? 

[Bodhisatya]

YiingShian:

 

The typical pressure usually lies between 4.3- 8 kg/cm2(g).  But also available are process cycles where PRe Purification handle incoming air at around 20 kg/cm2(g).  I have regenerated dual beds (Alumina and 13X) at around 230-250 degC with Heating and cooling time as 80 mins and 120 mins with satisfactory results.  Remember for proper regeneration, both the temperature and amount of regeneration gas available play a part.

 

Bodhisatya.

[YiingShian]

Bodhisatya:

 

Hi,

 

But according to this brochure i found the inlet condition can be at 7 bat gauge.  That is why i pick the high pressure.  Do you think PSA OR TSA is a more suitable system for such a large flow rate?

Attached Files

•  2935062812_CDplusBDplusXDplus_series_LR.pdf   7.19MB   36 downloads