5 replies to this topic

[Surya Budi]

Dear All,

 

I got a task for designing an air purification unit for a small air separation plant as my on job training task. Here are some data I have

Feed air flow rate = 780 Nm³/h

Feed air composition : N2 = 78.118 mol%

                                    O2 = 20.95 mol%

                                    Ar = 0.932 mol%

Feed air pressure = 7 barA

Relative humidity = 90%

 

Adsorber data

Type = TSA

Adsorbent type = Molecular Sieve 13X

Bed density = 650 kg/m³ (manufacturer data)

Adsorption time = 4 h

Adsorbent productivity = about 3 Nm³/kg.h (sampled from existing company purification unit)

 

Following the suggestion from "Industrial Gas Handbook" by Frank G. Kerry, the gas velocity through the bed should be around 10 cm/s during adsorption and the minimum quantity of adsorbent is 50 kg per 1000 Nm³/h of process air flow per 1 hour of adsorption

 

The adsorbent requirement:

Based on existing unit = 260 kg

Based on Kerry = 156 kg

 

Bed volume:

Based on existing unit = 0.4 m³

Based on Kerry = 0.24 m3

 

I calculated the superficial velocity based on the existing unit bed volume, 10 cm/s could be achieved by setting the H/D to 0.1. The velocity through the bed should be higher than 10 cm/s.

Trying to pursue 10 cm/s, I tried to split the flow into 2 until 4 parallel bed but the H/D still low, 0.25 for 4 beds in parallel.

Comparing to our existing purification unit, the superficial velocity is much higher, around 70-90 cm/s (I could not share the data of our existing unit)

 

Could someone give me some guidance on this problem? I attached my calculation.

 

Regards 

Attached Files

•  APU.xls   24KB   61 downloads

[Art Montemayor]

Surya:

 

I can give you some experienced guidance on the design and fabrication of an adsorbent dryer.  I've done it before for compressed air (for air separation units as well as for instrumentation service) and other gases.  However, you have to furnish specific information in order for me to supply you with specific comments, answers, and recommendations.

 

If you have an existing adsorbent dryer presently working in your facility it surely is not asking too much for you to furnish all the detailed design information on it such as: the number of beds, the diameter of the beds, the height of the adsorbent bed, the type of adsorbent used, the product dew point obtained, the type of NEMA TSA cycle that you employ, the type of regeneration cycle you use as well as the regen gas, its max. temperature and the final temperature of the adsorbent bed achieved before cooling.  This is not proprietary information.  Everyone in the business has an adsorption dryer and I could easily guess the data, but why should I speculate if it is available?

 

Please refer to your attached workbook (which I've renamed) and the information I've included to it.  I will include more pertinent information to it in future revisions if this thread continues and you furnish additional basic data.   Also read and study the "How to" paper on adsorption units' design.

 

Also, you title this thread "Air Purification" and not Air Drying".  Yet you only address the removal of water.  Are you also proposing to remove CO2 as well with the Mol Sieves?  If so, then please state it as such.  This is important data to know.

 

Await your reply.

 Air Adsorption Dryer.xls   90.5KB   96 downloads

 A How-to-Guide for Adsorber Design.pdf   536.46KB   110 downloads

[Surya Budi]

Dear Art,   Thank you for your reply. I am sorry for the lack of information. I try to furnish the detailed data but for some data I still wait information from our plant. For now, please find the data attached.   Yes, this purification unit should remove CO2 and water. Inside the attachment I state the input and output condition for CO2 and water. I also tried to do some more calculation as per your note to calculate based on water removed.   Regards.      

Attached Files

•  Air Adsorption Dryer.May20.xls   109.5KB   52 downloads

Edited by Surya Budi, 20 May 2013 - 10:06 PM.

[Bodhisatya]

Being Associated with Air Separation Industry am following this thread with great interest . Referring to the Pre-Purification Units that I have operated the Superficial velocity maintained is around 0.18 m/s with H/D ratio around 1.15 .

 

The Vessel is a vertical one with two layer of adsorbents ,lower being Alumina and the upper one is Mol Sieve separated by a Loose Separation screen.The Feed Air flow is from bottom to Top.

 

After operating the Vessel for quite a time we opened the vessel for certain inspection.Found that the loose separation screen separating two layers folded round the corner (Adjacent to Vessel Wall),resulting in small mixing of two layers.Telling you this history is to know what sort of Separation barrier are you considering while designing this APU.Any Details will be of great help.

 

Also will like to know from Art Sir ,what effect does this mixing of Adsorbents will have on the Dry Air at APU exit. In spite of the mixing I got Air Spec as per Design (Dew Point and CO2 Conc.).The Vessel was in operating for nearly 1 year.

 

Regards

Bodhisatya.

[Surya Budi]

Dear Bodhisatya,

 

Thank you for your interest and shared experience. Some of our plant also use two layers of adsorbent though not as many as the one that use one layer adsorbent. The configuration also activated alumina at the bottom and molecular sieve at the top with feed air flowing bottom up.

Do you have any suggestion for my problem? 

 

Regards.

[Surya Budi]

I tried to calculate based on CO2 adsorption isotherm data. But result in ridiculous volume.

Please check the updated spreadsheet.

 

Regards.

Attached Files

•  Air Adsorption Dryer.May22.xls   180.5KB   72 downloads