7 replies to this topic

[hannahpoole89]

Hi,

I am a final engineering student and i am designing a pressure swing adsorption and i need your help!

I have to submit my report next week and have wasted 3 weeks searching into this.I have read every article/book on design but no luck at all.

All articles i read give a series of equations and isotherm graphs but nothing i read tells you a step to step process on how to find the size of an adsorption column.All the information i have is the flowrate of air into the PSA which is 4000 kg/hr which means 2000kg/hr into each of the adsorption columns.I want to adsorb nitrogen as oxygen is my desired product and to do this  i will use a LiAgX catalyst which is a 13X catalyst.

I currently have an isotherm of the adsorption of nitrogen on the 13x catalyst.

what do i do after this?

how do i find the mass of zeolites needed?and the diameter and length of teh adsorption column?and which equations shall i use?

i will be sooo thankful for any help

[modgasman]

Try this book 'Pressure Swing Adsorption, VCH Wiley, 1994'

Let me know if you can't find it.

Also see attached file, although very brief, it seems to shed some light on your problem.

 

All the best

 

Attached Files

•  AdsorberDes2.pdf   536.46KB   404 downloads

Edited by modgasman, 04 March 2013 - 11:45 AM.

[Art Montemayor]

Hannah:

 

You are fighting an uphill battle – but not because you haven’t found the “correct” reading material.   You seem to have all the wrong ideas about the basic, pressure swing adsorption process.

 

If, as you say, you are trying to feed 4,000 kg/hr of air into an adsorption unit in order to selectively remove the nitrogen, leaving an oxygen-rich stream - then you certainly are not going to do what you describe: “which means 2,000 kg/hr into each of the adsorption columns.  I want to adsorb nitrogen as oxygen is my desired product and to do this i will use a LiAgX catalyst which is a 13X catalyst”.

 

If you spend some time in basically understanding the workings and logic of the fixed bed adsorption process, you will discover that a minimum of two beds are used to carry out the process:  one bed adsorbs while the other(s) are undergoing regeneration by desorption using a depressurization and purge waste gas stream.  Before the adsorption bed is depleted, the regenerated bed must be put into service and the roles are reversed.  Therefore, if you intend to adsorb 4,000 kg/hr of air, it means you will have to put that amount (and NOT 2,000 kg/hr) into each of the adsorption columns.  That is basic logic. 

 

Additionally – and a very important item – the adsorbent employed to selectively adsorb a component is just that – an adsorbent – and certainly NOT A CATALYST.  The adsorbent does not take part in a chemical reaction.  In fact, there is no chemical reactions involved in adsorption.  The ability to selectively bind one component on the surface of the adsorbent is very reversible – by using heat, vacuum, or a combination.

[modgasman]

Hannah,

I have a step by step procedure for designing an adsorber for you. Send me a message to my inbox  and I'll send u a copy.

All the best

Edited by modgasman, 11 September 2013 - 04:25 AM.

[frtcnby]

Hi All,

 

I am struggling with the same problem. I know, a year passed but i hope someone will se it. I need a step by step designing sample.

 

Thanks for any help

Edited by frtcnby, 16 May 2014 - 02:53 PM.

[Leonardo TD]

hi frtcnby,

 

please share if you found any help.  

 

thank you.

[clarkr3000]

There really is no one size fits all solution to adsorber design. It all depends on the constraints that you have for the system you are trying to design. If you are trying to separate O2/N2 from air what purity do you want? What is the amount of recovery of the feed? Purity and recovery are two different issues. What pressure is the feed going to be? You have to decide that based on the adsorbent isotherms. Can you run at lower pressure? That will come at the expense of recovery running at higher pressure increases the mechanical energy demand. Also, be very careful when using isotherms from literature as zeolites can vary widely in performance from manufacturer to manufacturer. Your best course of action in the design of your system is to obtain some samples of the sieves you want to use an perform a bench scale test to determine their performance. Once you have that information you can begin the design. I assume you have a product pressure in mind, so you can now take the isotherm and determine the working capacity of the adsorbents. ModGasMan left a good attachment that can give you a back of the envelope approach. Read it and I think you will be able to go from there.

[Art Montemayor]

The subject of adsorption and the need of a design procedure has been a topic that has been discussed many times in our forums - particularly the Student Forum.

 

I have uploaded a document titled "A How-to-Guide for Adsorber Design" many times in the past.  It is approx. 500 kb in size and goes through the design steps in a detailed manner.   If only you guys would use your time and effort in going through our SEARCH engine, you would find exactly what you describe as your need.  I suggest you do that and you will have your answer.