8 replies to this topic

[Harie]

Hi, 

I've never had experience with design and I'm having difficulty finding a starting point from textbooks. I have seen many references to Gas purification by Kohl here but unfortunately i do not have access to it. The only book I'm using as a guide is Coulson and Richardson but its not being of so much help.

 

I would really appreciate it if i could get help with starting the design of the absorber using MEA.

 

Thanks in advance. 

[breizh]

Let you try the search Function (top right) , This subject is very much covered in this forum , in particular by Art ,one of our administrator .

I guess you did some investigation using Google !

Hope this helps

Breizh

[Harie]

Thanks a lot Breizh. 

[Art Montemayor]

 

Harie:

As a chemical engineering student, the first thing you should learn on how to resolve engineering problems is to help yourself, not hinder yourself or create obstacles.  The best and most efficient way to help yourself resolve problems is to communicate correctly and efficiently.  By doing so, you can convey your problem and issues to others and thereby obtain their experiences and efficient help.

 

By trying to define your problem in the title of this thread you have made a very inefficient and wrong attempt at obtaining help.  The title of a thread is not the place where you define what help you need.  It is in the thread itself that you are supposed to explain what your problem is and what you need.  That is a very bad and poor way to communicate that only shows sloppiness and a poor attitude or attempt to explain what you need.   Engineers are supposed to be trained to communicate in specific, efficient, and effective ways that enable them to resolve problems quickly and correctly.

For example, if you have any oxygen present in a gas flow  together with CO₂ and you are trying to remove the CO₂, the worst thing you can do is to use an Amine solution – such as MEA, DEA, MDEA, etc..  The amines cannot tolerate any exposure to oxygen without degrading into very corrosive acidic compounds that will make your process a total failure.  DON’T DO IT!

 

Communicate in a detailed, accurate, and specific manner and you won’t make these kind of ignorant mistakes.  Please explain what you are trying to do and what you have as your total basic data.  It is sad that you have to receive this kind of advice up front, but believe me:  it is better you hear this from me than from your instructor who is probably expecting much better results from you - especially if you are attending a very serious and expensive university.

 

 

There are other ways to remove CO2 beside using amines.  But you have to accurately describe what you want to do or don't understand.

 

[Harie]

Thank you Art.

 

I'm designing a packed bed absorber for the removal of CO2 from an incoming stream of ethylene, oxygen, nitrogen and carbon dioxide. 

 Inlet temperature of the incoming gaseous stream = 40oC with flowrate 150027.7 kg/day

 Outlet temperature of the gaseous stream = 38oC with flowrate 147893.8 kg/day

 The process is at atmospheric pressure.

 I found out instead of MEA i could use Potassium carbonate or Sodium hydroxide. Which of the two better at absorbing?

 

I started the thread because i needed help with how to start the design of the absorber.

 

Thank you. 

[Art Montemayor]

Harie:

 

Good, now you are headed in a logical and rational direction.  There are other ways to separate the CO2 from a gaseous stream besides using an Amine process.  To reinforce your decision on the correct or best process, let's just state what these available processes are:

1. Other absorbents.  The Hot Pot process comes to mind.
2. Adsorption.  This becomes a non-practical process when dealing with very large gas flows - such as you seem to have.
3. Cryogenics.  In your case, you would "freeze out" the CO2 before liquefying the ethylene and oxygen.  Therefore, this is not a possibility.  (Besides, what is oxygen doing mixed with your ethylene?   I hope you have considered that this is a potential flammable and explosive mixture...)  Why aren't you being specific and giving your detailed gas stream compositions - both the raw feed and the expected product?

You really can't make much head way in fixing the correct process to employ without consulting with Kohl and Neilsen (Fred Reisendfeld died).   Presently, "Gas Purification" is the cornerstone of the gas processing literature.  You must obtain a copy of this book if you expect to make a success of your project.  You can certainly buy the latest edition on the Web and that is what I recommend you do right away.

 

From what little information you have doled out, I would guess that the Hot Pot process is your best candidate for now.

[kyleengineer]

Good question Waqar aka Harie 

[Art Montemayor]

Harie:
 

Read and study the attached presentation on acid gas removal design and operation by Majid Abdi.  It is one of the most detailed and well-presented discussion on this topic that I have read.

 

In it you will find answers to what your questions and details on what I have mentioned.

 Design & Operation of Acid Gas Removal Processes.docx   4.25MB   155 downloads

[Harie]

Thanks a lot Art.

 

The main project is the production of VAM and the oxygen in the ethylene stream is from the air after the reaction of VAM in the reactor. The gas stream compositions are (calculations were done with MEA as the absorbent then)

Inlet stream 

Ethylene 102869.9 kg/day

Oxygen 3758.899 kg/day

Nitrogen 41243.47 kg/day

Carbon dioxide 2155.384 kg/day

 

Outlet stream 1(assuming 99% efficiency of MEA )

 

Ethylene 102869.9 kg/day

Oxygen 3758.899 kg/day

Nitrogen 41243.47 kg/day

Carbon dioxide 21.553 kg/day

 

Outlet stream 2

Mea 9860.881 kg/day

Carbon dioxide 2133.83 kg/day

 

I considered the cryogenic process but my supervisor suggested i rather use a more economic process.