1 reply to this topic

[Roel]

Hi guys! I'm a Chemical Engineering student at University of the Philippines.

 

 

I'm currently designing a packed bed gas absorption for CO2 using Monoethanolamine (MEA)

I have tons of questions regarding this topic. BUut before that, I would like to post the given/conditions that I am currently doing.

 

1. Gas absorption by packed bed.

 

2. CO2 feed using reaction of Baking soda and vinegar (Not from a combustion reaction)

 

3. 15-30% MEA solution (I am using plastic column and packing materials so corrosion is minimal)

 

4. Lab scale absorption column (no more than 1.5m of column) <-- for study purposes only not industrial.

 

5. VLE data from Aronu (ScienceDirect.com

 

6. Gas absorption with MEA regeneration using heating coils (Not stripping and no steam)

 

7. The goal is to have a steady state equipment with MEA regeneration. The recycled MEA is put back to the column.

 

 

Here are my questions:

 

1. Is it possible to use plastic column and packing material? Won't MEA destroy it?

 

 

2. Is it possible to regenerate MEA using heating coils only and not stripping and water? I saw some chemical reactions involving CO2 loaded MEA and H2O. Is steam needed for regeneration? Is heating coil enough for regeneration?

 

 

3. Since I am using a homemade packing material. I won't be able to calculate pressure drop and diameter using Generalized Pressure Drop Correlation because manufacturers provide specific data per packing material. Given that, how do I calculate the Pressure drop and Diameter of column? I need those two so that I will know if the diameter is feasible of absorption.

 

 

4. According to Foust (1980), Height of Column is equal to Number of Transfer unit (NTU) multiplied by Height of transfer unit (HTU).

height = NTU*HTU

 

 

I have a way of calculation NTU using integration and numerical methods. However HTU is not easily calculated because Total Gas-phase mass transfer coefficient (Ky) cannot be determined. How do i get the values of Ky? Is there another way to calculate HTU other than using Ky?

Thank you very much! I am new to chemical engineering designs so I have a lot of questions. If there's any data missing just tell me I'll add.

Here's my proposed equipment diagram

 

Edited by Roel, 13 April 2015 - 08:03 AM.

[Art Montemayor]

Roel:

 

You probably have “tons” of questions regarding this topic because you haven’t read nor studied the necessary textual information on the subject of using amine solutions (especially MEA) for the removal of CO₂.  You should have already read and studied carefully all the material found in such classic literature as:

• “Gas Purification” by Kohl & Neilsen;
• The GPSA Engineering Data Book;
• “Gas Conditioning and Processing” by John Campbell
• A “ton” of material on the subject to be found in our Forums’ Archives, obtainable through use of our Search Engine.

All your questions are prone to generate even more, detailed questions once answered.  But I’ll briefly tell you that you need to furnish more critical information such as feed gas composition, your specific assignment (is it a pilot plant? A computer simulation? A study for academic purposes? Etc., etc.), your flow rates and stream conditions, and your algorithms (or detailed calculations).  It is only in that way that our Forum members can answer your queries in an accurate and detailed manner that could be of use to you.  Generalizing your query will only generate generalizations - which are useless for resolution to a real, practical engineering problem.

 

General answers to your questions are:

1. Yes, you can use plastic tower packings for an MEA solution.  However, you have to select the proper plastic to withstand the process conditions - it isn’t just the class of material that is important; it’s the specific plastic.  Depending on the specific process you select, you may be better off with SS packing - specifically structured packing.
2. Yes, you can regenerate an MEA rich solution without the use of steam.  You can employ a direct-fired reboiler to achieve this.  This was originally done by the inventors of the MEA acid gas process, The Girdler Corp.  I will post the detailed information in my next post if you are interested in finding out more about how this was done.  There are draw-backs (trade offs) to the method, however.
3. Relatively accurate pressure drop predictions through packed beds are obtained using the packing manufacturer’s information and data.  If have your own packing, then you have to generate that information.  Experience will tell you how much to estimate; but since you don’t have experience, then you have to “guess-timate” the pressure drop.
4. If you read and study the texts and literature I’ve recommended you will find that the process sizing of CO₂ absorbers - as well as strippers - is done empirically, using experience and field data.  You don’t have either, so you must resort to using basic recommended sizes and since you fail to give all the process information and data, the Forum members can’t estimate your needed sizes.

The basic flow diagram you furnish shows that you lack the background and sufficient study to understand the process.  This is a step that almost all students (in order to take a short cut and avoid time-consuming study) erroneously and ignorantly avoid or sidestep - leading up to an erroneous understanding and ultimate product.  You must DO YOUR HOMEWORK FIRST.  By this, I mean that you must do the basic hard work of studying and knowing all there is to know about the process you propose to “design”.  To avoid doing the up-front hard work is to cheat yourself and leads to producing a lacking and/or erroneous engineering report.  You must learn all that you can gather about your topic; engineers are not paid for mistakes.  Engineers are fired if they make basic mistakes.  They MUST know what it is that they are resolving and proposing.  For example, your diagram shows that the rich MEA solution goes to a “heater”.  That is completely wrong.  It should go through a heat exchanger and thence to an MEA Stripper tower, and subsequently through a reboiler of some sort.  How you furnish heat to that tower is something you must show - as well as all heat transfer equipment.

 

Await your return reply.