4 replies to this topic

[gayathri]

Hi...My project work as a trainee is to design cryosorption device using zeolite ms 5A at liquid nitrogen temperature for the separation of hydrogen isotopes in tritium extraction system.The duration of my project is 5 months.Being a fresher I dont have much exposure to industrial adsorption columns design.So I kindly request experts over here to guide me as to how I should proceed for my design of adsorber columns....

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Edited by gayathri, 24 February 2010 - 12:24 AM.

[djack77494]

gayathri,
I'm sorry to say that you are most unlikely to receive your requested help. It's not that there isn't interest in helping you; it's just that this is a very, very specialized area and any experience your readers might have in designing column would be vastly different from what is needed in your application. Don't get hung up calling your "refining" equipment to be "a column". What it is is a unit operation. You may have many in series to reach your objective. Abosrption columns even of much more conventional design are not typically solved using general process simulators, and I would certainly not recommend one in your case. You need to simply figure out the governing equations and "hammer" them into a model that will predict performance. Excel or something similar might well be your best choice.

[ankur2061]

[quote name='gayathri' date='05 February 2010 - 08:17 AM' timestamp='1265344044' post='36054']
[quote name='djack77494' date='04 February 2010 - 01:24 PM' timestamp='1265308499' post='36050']
Thanks for your reply Mr.Djack...
It is an project for a duration of only 5 months and I ve to design 5 equipments.No experimental procedures need to be done....So I just need to submit an approach to design with some calculations..Since am a fresher with no experience in chemical plant design I just need to know how a design is being proceeded....An overview with which I can try it out....If some calculation procedures could be sent to me Ill be very grateful....
Pl do suggest some books for refrences...
Thanks a lot.......
[/quote]

Gayathri,

Three good books to get you started are:

GPSA Engineering Databook, 11th Edition-1998

Applied Process Design, Ernest E. Ludwig, 4th Edition (Vol . 2 )

Handbook of Chemical Engineering Calcualtions, Nicholas P. Chopey

These should really help you to get started.

Regards,
Ankur

[kkala]

Service Moisture trapping from purge gas
Adsorber type Mol. Sieve 5A
Bead size 3 mm
Capacity 49 gm of moisture
Helium Flow 31.5 Nm3/hr
Operating temperature 30 oC
Operating pressure 0.12 MPa
Moisture content in purge gas 11.5 ppm
Size 200 mm dia x 250 mm height
Regeneration time 7 days
Regeneration temperature 250 oC
Regeneration heater 1 kW
Insulation type Hot
Quantity 2

Another reference for adsorption is G. G. Brown's "Unit Operations", Wiley 1950, Chapter 27 - Adsorption. Though I have no knowledge in adsorption, understanding is as follows.
1. The task concerns dehumidifying (to what extent? probably close to 100%) of 31.5 Nm3/h of He at almost atmospheric pressure, using two cylinders containing beds of molecular seal No 5A. Info on the latter can be found at <http://www.tower-pac...ular_sieve.htm>, it is an alkali alumino silicate substance (may be improved version of Al2O3 or silica gel, used as desiccants). For any data needed, you can ask suppliers of No 5A molecular seal.
2. One bed is in operation, the other in regeneration. The period of 7 days fits this scheme, since "saturation" of operating bed seems to occur also in 7 days: Moister with He is (31.5/22.414)*(11.5/1000000)*18*1000=0.291 g/h, so the bed is exhausted in 49/0.291=168.4 h~7days.
3. Next steps can be (a) check thickness of No 5A molecular seal required (3 mm?) - most important. (β)check time needed for regeneration at 250 0C. © check adequacy of 1 kW regeneration heater by estimating heat loses. I assume spirit of exercise is to make estimates by yourself, but you may contact suppliers for verification / help.

Edited by kkala, 06 February 2010 - 03:14 PM.

[kkala]

As for now ive calculated the
Amount of adsorbent required(by using adsorption isotherm data from literature)
The volume of packed bed,its height,diameter,residence time of purge in the column.
What should be my next step....the time required for regeneration has already been calculated.
How to proceed with the regeneration in temperature swing adsorption process??
CAn I proceed with HTU and NTU calculations??

As said before, I had no knowledge on adsorption, even though I see G. G. Brown (ref of 6 Feb 2010 post) treating its simple cases more or less like distillation (diffusion not detected). But I understand now that you have specified everything by yourself (you write "no input data s given") and I would like to express few comments from an ignorant viewer, that may or may not be useful.
1. Bed size of 3 mm seems too thin, "hole" or dilute stack of desiccant may be created, resulting in serious loss of dehydration efficiency. A generous decrease of cylinder diameter (now 200 mm) may cure it (if applicable). You may be afraid of desiccant entrainment due to increase of gas velocity (now ~ 0.3 m/s). We faced a similar case of fine catalyst by enclosing its bed in the cylinder with two pieces of finer mesh.
2. Swing period is usually 10-20 minutes, not a week (see http://www.esselinkbv.com/descr.html). If it is a week, a "He moisture switch high" alarm (based on online moisture analyser signal) can warn the operator for manual change by manipulating the proper valves. I do not know reliability of online moister analysers, but it is probably high enough (so no "voting" seems necessary). If you want to avoid operator's action, you can automatically isolate the spent desiccant (on He moister switch HH) and open the valves of fresh desiccant, with event recording to the control room.
This under the assumption that this operation is rather critical (nuclear). In a common plant (refinery, alumina) similarly drying instrument air, only swing would probably occur at the proper time (i.e. when swing period is exhausted, so desiccant approaches saturation).

Hope somebody else will advise specifically on adsorption.