Jump to content



Featured Articles

Check out the latest featured articles.

File Library

Check out the latest downloads available in the File Library.

New Article

Product Viscosity vs. Shear

Featured File

Vertical Tank Selection

New Blog Entry

Low Flow in Pipes- posted in Ankur's blog

Air Drying By Adsorption


This topic has been archived. This means that you cannot reply to this topic.
2 replies to this topic
Share this topic:
| More

#1 Niels

Niels

    Brand New Member

  • Members
  • 2 posts

Posted 04 December 2009 - 09:32 AM

Hello,

I am a newbie on this forum. My mother languages is Dutch and my English isn’t very good, but I give it a try.

I would like to design a adsorber for drying wet compressed air.

The total air current (to be dried) is 80 m3/h (referred to 35 °C and 8 bar(a)).
The desirable pressure dewpoint is -40 °C by a temperature of 35 °C.
During a adsorption process of 4 hours, there should be removed 10,76 kg. H2O to reach the desirable pressure dewpoint.
I would use the desiccant Activated Alumina 2-5 mm.

I did the following assumptions:
The flow velocity referred to the open cross-section of the adsorber: 0,15 m/s ("Separation Processes (Jean-Pierre Wauquier)" --> Between 0,1 and 0,3 m/s for gases)
The effective capacity of Activated Alumina: 7 kgH2O / 100 kg. Activated Alumina ("Separation Processes (Jean-Pierre Wauquier)" --> Between 4 and 7 kgH2O / 100 kg. Activated Alumina)

Calculations:
> From the air current and the flow velocity, we can calculate the diameter of the adsorber: 0,434 m.
> Next we can calculate the needed mass of adsorbent: (10,76/7)*100 = 153,71 kg. Activated Alumina.
> With a bulk density of 752 kg/m3 we have a adsorbent volume of 0,20 m3.
> This results in a bed height of 1,35 m. and a L/D ratio of 3,12 which is between the recommended ratio of 1 and 4 for gases)

My questions about this:
  • Is this a correct calculation (Assuming that the assumptions are correct)?
  • Where can I find/calculate the effective contact time between air and adsorbent?
  • I’ve did a assumption about flow velocity, but how can I calculate the actual needed flow velocity?
  • Can anyone tell me where I can find the effective capacities of different desiccants? And where is this capacity depended on?
  • How can I calculate the operating pressure-drop of the adsorption process?
  • Can anyone give me tips or something which I can take into account?
I hope somebody can help me with (some of) these questions.

Kind regards,
Niels

#2 Art Montemayor

Art Montemayor

    Gold Member

  • Admin
  • 5,780 posts

Posted 05 December 2009 - 12:20 AM



Niels:

I have, in the past done a lot of consulting and posting on these forums regarding this specific subject. The first thing I recommend is that you spend some of your time doing the needed research through our forums using our Search Machine. This will answer a lot of your basic questions and orient you as to what are the basics in designing an adsorption type of dryer. There are quite a lot of variables and facts that you are not touching on (and obviously not aware of) that you need in order to "design" and adsorption bed. As a student, please be specific and direct to the point. We waste a lot of valuable time and effort trying to help out students who simply will not come forward and be honest and candid in their queries. If you are doing a homework problem, admit it. If you have been assigned this problem in a course, come out and state it. We are not mind readers; we need all the basic data and scope of work that you already know and are keeping from us. The more you tell us, the more you will receive and the easier it will be for everyone involved.

I presently find myself waiting for an Air France flight into Paris and later on to Houston, Texas - so I am writing this in the Madrid Airport VIP lounge and don't have the facilities of my notes, files, or office. I will be busy for the next 40 days, celebrating Christmas and taking a quick trip to Amsterdam before Christmas Eve. However, I can offer the following responses to your direct questions:


1) Your calculation is not correct; you fail to employ the fact that any adsorbent will "age" or suffer in sorptivity due to contamination, use, regeneration, attrition, and other factors. The main point is that your sorptivity design figure of 7 lb water/100 lb of Activated Alumina depends on your specifically setting other factors, such as type of Activated Alumina, reactivation process type & temperature, pressure applied, potential contaminents, etc. You fail to specifically identify what Mr. Wauqier has set as the basis for his figure. I personally know this figure is a general, generic figure. No one would design with this figure unless he/she knew the other factors behind it. I know nothing of Mr. Wauqier and must assume that he knows what he is talking/writing about. Depending on the factors and circumstances, I usually employ a figure of approximately 4-5 lb water/100 lb of Activated Alumina -- but that depends on a lot of things.

2) Why would you want to know the "effective" contact time? The superficial velocity suffices to specify that indirectly.

4) For effective, practical design sorptive capacities of any adsorbent, no one is better qualified than the actual manufacturer himself.

5) For pressure drop calculations, find the applicable threads in our forums. I have discussed and identified the method in past threads.

6) For understanding adsorption and design of a dryer, read Kohl & Reisenfeld's "Gas Purification", the GPSA Engineering Databook, and other references. The subject of other details will take a very long thread and my plane is arriving.

Be specific and answer my request for ALL the basic data and full description of your scope of work, and I might be able to help you with the specifics in the future. I will be tied up with my #1 priority in life - my granddaughters - during these Christmas Holidays, so I might not have much time to spend on this forum. However, you failed to furnish your time table (part of basic data), so I can't comment on that. However, I will do what I can when I have the time available.

Look forward to your response and data/scope.


#3 Niels

Niels

    Brand New Member

  • Members
  • 2 posts

Posted 09 December 2009 - 03:53 AM

Hello Art Montemayor,

Thanks for your quick reply. This is a question for my internship, but I've family issuses at the moment, I'm sorry for that. I am not in the opportunity to answer at this moment. I would answer within a week or so.

Kind regards,
Niels




Similar Topics